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 </pre><pre class="rust ">
 <span class="comment">// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT</span>
 <span class="comment">// file at the top-level directory of this distribution and at</span>
 <span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
 <span class="comment">//</span>
 <span class="comment">// Licensed under the Apache License, Version 2.0 &lt;LICENSE-APACHE or</span>
 <span class="comment">// http://www.apache.org/licenses/LICENSE-2.0&gt; or the MIT license</span>
 <span class="comment">// &lt;LICENSE-MIT or http://opensource.org/licenses/MIT&gt;, at your</span>
 <span class="comment">// option. This file may not be copied, modified, or distributed</span>
 <span class="comment">// except according to those terms.</span>

 <span class="doccomment">/*!
 This crate provides a regular expression parser and an abstract syntax for
 regular expressions. The abstract syntax is defined by the `Expr` type. The
 concrete syntax is enumerated in the
 [`regex`](../regex/index.html#syntax)
 crate documentation.

 Note that since this crate is first and foremost an implementation detail for
 the `regex` crate, it may experience more frequent breaking changes. It is
 exposed as a separate crate so that others may use it to do analysis on regular
 expressions or even build their own matching engine.

 # Example: parsing an expression

 Parsing a regular expression can be done with the `Expr::parse` function.

 ```rust
 use regex_syntax::Expr;

 assert_eq!(Expr::parse(r&quot;ab|yz&quot;).unwrap(), Expr::Alternate(vec![
     Expr::Literal { chars: vec![&#39;a&#39;, &#39;b&#39;], casei: false },
     Expr::Literal { chars: vec![&#39;y&#39;, &#39;z&#39;], casei: false },
 ]));
 ```

 # Example: inspecting an error

 The parser in this crate provides very detailed error values. For example,
 if an invalid character class range is given:

 ```rust
 use regex_syntax::{Expr, ErrorKind};

 let err = Expr::parse(r&quot;[z-a]&quot;).unwrap_err();
 assert_eq!(err.position(), 4);
 assert_eq!(err.kind(), &amp;ErrorKind::InvalidClassRange {
     start: &#39;z&#39;,
     end: &#39;a&#39;,
 });
 ```

 Or unbalanced parentheses:

 ```rust
 use regex_syntax::{Expr, ErrorKind};

 let err = Expr::parse(r&quot;ab(cd&quot;).unwrap_err();
 assert_eq!(err.position(), 2);
 assert_eq!(err.kind(), &amp;ErrorKind::UnclosedParen);
 ```
 */</span>

 <span class="attribute">#<span class="op">!</span>[<span class="ident">deny</span>(<span class="ident">missing_docs</span>)]</span>
 <span class="attribute">#<span class="op">!</span>[<span class="ident">cfg_attr</span>(<span class="ident">test</span>, <span class="ident">deny</span>(<span class="ident">warnings</span>))]</span>

 <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span> <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">quickcheck</span>;
 <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span> <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">rand</span>;

 <span class="kw">mod</span> <span class="ident">literals</span>;
 <span class="kw">mod</span> <span class="ident">parser</span>;
 <span class="kw">mod</span> <span class="ident">unicode</span>;

 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ascii</span>;
 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">char</span>;
 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cmp</span>::{<span class="ident">Ordering</span>, <span class="ident">max</span>, <span class="ident">min</span>};
 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>;
 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">iter</span>::<span class="ident">IntoIterator</span>;
 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ops</span>::<span class="ident">Deref</span>;
 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">result</span>;
 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">slice</span>;
 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">u8</span>;
 <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">vec</span>;

 <span class="kw">use</span> <span class="ident">unicode</span>::<span class="ident">case_folding</span>;

 <span class="kw">use</span> <span class="self">self</span>::<span class="ident">Expr</span>::<span class="kw-2">*</span>;
 <span class="kw">use</span> <span class="self">self</span>::<span class="ident">Repeater</span>::<span class="kw-2">*</span>;

 <span class="kw">use</span> <span class="ident">parser</span>::{<span class="ident">Flags</span>, <span class="ident">Parser</span>};

 <span class="kw">pub</span> <span class="kw">use</span> <span class="ident">literals</span>::{<span class="ident">Literals</span>, <span class="ident">Lit</span>};

 <span class="doccomment">/// A regular expression abstract syntax tree.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// An `Expr` represents the abstract syntax of a regular expression.</span>
 <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
 <span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Expr</span> {
     <span class="doccomment">/// An empty regex (which never matches any text).</span>
     <span class="ident">Empty</span>,
     <span class="doccomment">/// A sequence of one or more literal characters to be matched.</span>
     <span class="ident">Literal</span> {
         <span class="doccomment">/// The characters.</span>
         <span class="ident">chars</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">char</span><span class="op">&gt;</span>,
         <span class="doccomment">/// Whether to match case insensitively.</span>
         <span class="ident">casei</span>: <span class="ident">bool</span>,
     },
     <span class="doccomment">/// A sequence of one or more literal bytes to be matched.</span>
     <span class="ident">LiteralBytes</span> {
         <span class="doccomment">/// The bytes.</span>
         <span class="ident">bytes</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">u8</span><span class="op">&gt;</span>,
         <span class="doccomment">/// Whether to match case insensitively.</span>
         <span class="doccomment">///</span>
         <span class="doccomment">/// The interpretation of &quot;case insensitive&quot; in this context is</span>
         <span class="doccomment">/// ambiguous since `bytes` can be arbitrary. However, a good heuristic</span>
         <span class="doccomment">/// is to assume that the bytes are ASCII-compatible and do simple</span>
         <span class="doccomment">/// ASCII case folding.</span>
         <span class="ident">casei</span>: <span class="ident">bool</span>,
     },
     <span class="doccomment">/// Match any character.</span>
     <span class="ident">AnyChar</span>,
     <span class="doccomment">/// Match any character, excluding new line (`0xA`).</span>
     <span class="ident">AnyCharNoNL</span>,
     <span class="doccomment">/// Match any byte.</span>
     <span class="ident">AnyByte</span>,
     <span class="doccomment">/// Match any byte, excluding new line (`0xA`).</span>
     <span class="ident">AnyByteNoNL</span>,
     <span class="doccomment">/// A character class.</span>
     <span class="ident">Class</span>(<span class="ident">CharClass</span>),
     <span class="doccomment">/// A character class with byte ranges only.</span>
     <span class="ident">ClassBytes</span>(<span class="ident">ByteClass</span>),
     <span class="doccomment">/// Match the start of a line or beginning of input.</span>
     <span class="ident">StartLine</span>,
     <span class="doccomment">/// Match the end of a line or end of input.</span>
     <span class="ident">EndLine</span>,
     <span class="doccomment">/// Match the beginning of input.</span>
     <span class="ident">StartText</span>,
     <span class="doccomment">/// Match the end of input.</span>
     <span class="ident">EndText</span>,
     <span class="doccomment">/// Match a word boundary (word character on one side and a non-word</span>
     <span class="doccomment">/// character on the other).</span>
     <span class="ident">WordBoundary</span>,
     <span class="doccomment">/// Match a position that is not a word boundary (word or non-word</span>
     <span class="doccomment">/// characters on both sides).</span>
     <span class="ident">NotWordBoundary</span>,
     <span class="doccomment">/// Match an ASCII word boundary.</span>
     <span class="ident">WordBoundaryAscii</span>,
     <span class="doccomment">/// Match a position that is not an ASCII word boundary.</span>
     <span class="ident">NotWordBoundaryAscii</span>,
     <span class="doccomment">/// A group, possibly non-capturing.</span>
     <span class="ident">Group</span> {
         <span class="doccomment">/// The expression inside the group.</span>
         <span class="ident">e</span>: <span class="ident">Box</span><span class="op">&lt;</span><span class="ident">Expr</span><span class="op">&gt;</span>,
         <span class="doccomment">/// The capture index (starting at `1`) only for capturing groups.</span>
         <span class="ident">i</span>: <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span>,
         <span class="doccomment">/// The capture name, only for capturing named groups.</span>
         <span class="ident">name</span>: <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">String</span><span class="op">&gt;</span>,
     },
     <span class="doccomment">/// A repeat operator (`?`, `*`, `+` or `{m,n}`).</span>
     <span class="ident">Repeat</span> {
         <span class="doccomment">/// The expression to be repeated. Limited to literals, `.`, classes</span>
         <span class="doccomment">/// or grouped expressions.</span>
         <span class="ident">e</span>: <span class="ident">Box</span><span class="op">&lt;</span><span class="ident">Expr</span><span class="op">&gt;</span>,
         <span class="doccomment">/// The type of repeat operator used.</span>
         <span class="ident">r</span>: <span class="ident">Repeater</span>,
         <span class="doccomment">/// Whether the repeat is greedy (match the most) or not (match the</span>
         <span class="doccomment">/// least).</span>
         <span class="ident">greedy</span>: <span class="ident">bool</span>,
     },
     <span class="doccomment">/// A concatenation of expressions. Must be matched one after the other.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// N.B. A concat expression can only appear at the top-level or</span>
     <span class="doccomment">/// immediately inside a group expression.</span>
     <span class="ident">Concat</span>(<span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">Expr</span><span class="op">&gt;</span>),
     <span class="doccomment">/// An alternation of expressions. Only one must match.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// N.B. An alternate expression can only appear at the top-level or</span>
     <span class="doccomment">/// immediately inside a group expression.</span>
     <span class="ident">Alternate</span>(<span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">Expr</span><span class="op">&gt;</span>),
 }

 <span class="kw">type</span> <span class="ident">CaptureIndex</span> <span class="op">=</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span>;

 <span class="kw">type</span> <span class="ident">CaptureName</span> <span class="op">=</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">String</span><span class="op">&gt;</span>;

 <span class="doccomment">/// The type of a repeat operator expression.</span>
 <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Copy</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
 <span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Repeater</span> {
     <span class="doccomment">/// Match zero or one (`?`).</span>
     <span class="ident">ZeroOrOne</span>,
     <span class="doccomment">/// Match zero or more (`*`).</span>
     <span class="ident">ZeroOrMore</span>,
     <span class="doccomment">/// Match one or more (`+`).</span>
     <span class="ident">OneOrMore</span>,
     <span class="doccomment">/// Match for at least `min` and at most `max` (`{m,n}`).</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// When `max` is `None`, there is no upper bound on the number of matches.</span>
     <span class="ident">Range</span> {
         <span class="doccomment">/// Lower bound on the number of matches.</span>
         <span class="ident">min</span>: <span class="ident">u32</span>,
         <span class="doccomment">/// Optional upper bound on the number of matches.</span>
         <span class="ident">max</span>: <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">u32</span><span class="op">&gt;</span>,
     },
 }

 <span class="kw">impl</span> <span class="ident">Repeater</span> {
     <span class="doccomment">/// Returns true if and only if this repetition can match the empty string.</span>
     <span class="kw">fn</span> <span class="ident">matches_empty</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="kw">use</span> <span class="self">self</span>::<span class="ident">Repeater</span>::<span class="kw-2">*</span>;
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">ZeroOrOne</span> <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             <span class="ident">ZeroOrMore</span> <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             <span class="ident">OneOrMore</span> <span class="op">=&gt;</span> <span class="bool-val">false</span>,
             <span class="ident">Range</span> { <span class="ident">min</span>, .. } <span class="op">=&gt;</span> <span class="ident">min</span> <span class="op">==</span> <span class="number">0</span>,
         }
     }
 }

 <span class="doccomment">/// A character class.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// A character class has a canonical format that the parser guarantees. Its</span>
 <span class="doccomment">/// canonical format is defined by the following invariants:</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// 1. Given any Unicode scalar value, it is matched by *at most* one character</span>
 <span class="doccomment">///    range in a canonical character class.</span>
 <span class="doccomment">/// 2. Every adjacent character range is separated by at least one Unicode</span>
 <span class="doccomment">///    scalar value.</span>
 <span class="doccomment">/// 3. Given any pair of character ranges `r1` and `r2`, if</span>
 <span class="doccomment">///    `r1.end &lt; r2.start`, then `r1` comes before `r2` in a canonical</span>
 <span class="doccomment">///    character class.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// In sum, any `CharClass` produced by this crate&#39;s parser is a sorted</span>
 <span class="doccomment">/// sequence of non-overlapping ranges. This makes it possible to test whether</span>
 <span class="doccomment">/// a character is matched by a class with a binary search.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// If the case insensitive flag was set when parsing a character class, then</span>
 <span class="doccomment">/// simple case folding is done automatically. For example, `(?i)[a-c]` is</span>
 <span class="doccomment">/// automatically translated to `[a-cA-C]`.</span>
 <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
 <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">CharClass</span> {
     <span class="ident">ranges</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ClassRange</span><span class="op">&gt;</span>,
 }

 <span class="doccomment">/// A single inclusive range in a character class.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// Since range boundaries are defined by Unicode scalar values, the boundaries</span>
 <span class="doccomment">/// can never be in the open interval `(0xD7FF, 0xE000)`. However, a range may</span>
 <span class="doccomment">/// *cover* codepoints that are not scalar values.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// Note that this has a few convenient impls on `PartialEq` and `PartialOrd`</span>
 <span class="doccomment">/// for testing whether a character is contained inside a given range.</span>
 <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Copy</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">PartialOrd</span>, <span class="ident">Eq</span>, <span class="ident">Ord</span>)]</span>
 <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ClassRange</span> {
     <span class="doccomment">/// The start character of the range.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This must be less than or equal to `end`.</span>
     <span class="kw">pub</span> <span class="ident">start</span>: <span class="ident">char</span>,

     <span class="doccomment">/// The end character of the range.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This must be greater than or equal to `start`.</span>
     <span class="kw">pub</span> <span class="ident">end</span>: <span class="ident">char</span>,
 }

 <span class="doccomment">/// A byte class for byte ranges only.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// A byte class has a canonical format that the parser guarantees. Its</span>
 <span class="doccomment">/// canonical format is defined by the following invariants:</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// 1. Given any byte, it is matched by *at most* one byte range in a canonical</span>
 <span class="doccomment">///    character class.</span>
 <span class="doccomment">/// 2. Every adjacent byte range is separated by at least one byte.</span>
 <span class="doccomment">/// 3. Given any pair of byte ranges `r1` and `r2`, if</span>
 <span class="doccomment">///    `r1.end &lt; r2.start`, then `r1` comes before `r2` in a canonical</span>
 <span class="doccomment">///    character class.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// In sum, any `ByteClass` produced by this crate&#39;s parser is a sorted</span>
 <span class="doccomment">/// sequence of non-overlapping ranges. This makes it possible to test whether</span>
 <span class="doccomment">/// a byte is matched by a class with a binary search.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// If the case insensitive flag was set when parsing a character class,</span>
 <span class="doccomment">/// then simple ASCII-only case folding is done automatically. For example,</span>
 <span class="doccomment">/// `(?i)[a-c]` is automatically translated to `[a-cA-C]`.</span>
 <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
 <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ByteClass</span> {
     <span class="ident">ranges</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span>,
 }

 <span class="doccomment">/// A single inclusive range in a byte class.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// Note that this has a few convenient impls on `PartialEq` and `PartialOrd`</span>
 <span class="doccomment">/// for testing whether a byte is contained inside a given range.</span>
 <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Copy</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">PartialOrd</span>, <span class="ident">Eq</span>, <span class="ident">Ord</span>)]</span>
 <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ByteRange</span> {
     <span class="doccomment">/// The start byte of the range.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This must be less than or equal to `end`.</span>
     <span class="kw">pub</span> <span class="ident">start</span>: <span class="ident">u8</span>,

     <span class="doccomment">/// The end byte of the range.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This must be greater than or equal to `end`.</span>
     <span class="kw">pub</span> <span class="ident">end</span>: <span class="ident">u8</span>,
 }

 <span class="doccomment">/// A builder for configuring regular expression parsing.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// This allows setting the default values of flags and other options, such</span>
 <span class="doccomment">/// as the maximum nesting depth.</span>
 <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>)]</span>
 <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ExprBuilder</span> {
     <span class="ident">flags</span>: <span class="ident">Flags</span>,
     <span class="ident">nest_limit</span>: <span class="ident">usize</span>,
 }

 <span class="kw">impl</span> <span class="ident">ExprBuilder</span> {
     <span class="doccomment">/// Create a new builder for configuring expression parsing.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// Note that all flags are disabled by default.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-&gt;</span> <span class="ident">ExprBuilder</span> {
         <span class="ident">ExprBuilder</span> {
             <span class="ident">flags</span>: <span class="ident">Flags</span>::<span class="ident">default</span>(),
             <span class="ident">nest_limit</span>: <span class="number">200</span>,
         }
     }

     <span class="doccomment">/// Set the default value for the case insensitive (`i`) flag.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">case_insensitive</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">yes</span>: <span class="ident">bool</span>) <span class="op">-&gt;</span> <span class="ident">ExprBuilder</span> {
         <span class="self">self</span>.<span class="ident">flags</span>.<span class="ident">casei</span> <span class="op">=</span> <span class="ident">yes</span>;
         <span class="self">self</span>
     }

     <span class="doccomment">/// Set the default value for the multi-line matching (`m`) flag.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">multi_line</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">yes</span>: <span class="ident">bool</span>) <span class="op">-&gt;</span> <span class="ident">ExprBuilder</span> {
         <span class="self">self</span>.<span class="ident">flags</span>.<span class="ident">multi</span> <span class="op">=</span> <span class="ident">yes</span>;
         <span class="self">self</span>
     }

     <span class="doccomment">/// Set the default value for the any character (`s`) flag.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">dot_matches_new_line</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">yes</span>: <span class="ident">bool</span>) <span class="op">-&gt;</span> <span class="ident">ExprBuilder</span> {
         <span class="self">self</span>.<span class="ident">flags</span>.<span class="ident">dotnl</span> <span class="op">=</span> <span class="ident">yes</span>;
         <span class="self">self</span>
     }

     <span class="doccomment">/// Set the default value for the greedy swap (`U`) flag.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">swap_greed</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">yes</span>: <span class="ident">bool</span>) <span class="op">-&gt;</span> <span class="ident">ExprBuilder</span> {
         <span class="self">self</span>.<span class="ident">flags</span>.<span class="ident">swap_greed</span> <span class="op">=</span> <span class="ident">yes</span>;
         <span class="self">self</span>
     }

     <span class="doccomment">/// Set the default value for the ignore whitespace (`x`) flag.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">ignore_whitespace</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">yes</span>: <span class="ident">bool</span>) <span class="op">-&gt;</span> <span class="ident">ExprBuilder</span> {
         <span class="self">self</span>.<span class="ident">flags</span>.<span class="ident">ignore_space</span> <span class="op">=</span> <span class="ident">yes</span>;
         <span class="self">self</span>
     }

     <span class="doccomment">/// Set the default value for the Unicode (`u`) flag.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// If `yes` is false, then `allow_bytes` is set to true.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">unicode</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">yes</span>: <span class="ident">bool</span>) <span class="op">-&gt;</span> <span class="ident">ExprBuilder</span> {
         <span class="self">self</span>.<span class="ident">flags</span>.<span class="ident">unicode</span> <span class="op">=</span> <span class="ident">yes</span>;
         <span class="kw">if</span> <span class="op">!</span><span class="ident">yes</span> {
             <span class="self">self</span>.<span class="ident">allow_bytes</span>(<span class="bool-val">true</span>)
         } <span class="kw">else</span> {
             <span class="self">self</span>
         }
     }

     <span class="doccomment">/// Whether the parser allows matching arbitrary bytes or not.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// When the `u` flag is disabled (either with this builder or in the</span>
     <span class="doccomment">/// expression itself), the parser switches to interpreting the expression</span>
     <span class="doccomment">/// as matching arbitrary bytes instead of Unicode codepoints. For example,</span>
     <span class="doccomment">/// the expression `(?u:\xFF)` matches the *codepoint* `\xFF`, which</span>
     <span class="doccomment">/// corresponds to the UTF-8 byte sequence `\xCE\xBF`. Conversely,</span>
     <span class="doccomment">/// `(?-u:\xFF)` matches the *byte* `\xFF`, which is not valid UTF-8.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// When `allow_bytes` is disabled (the default), an expression like</span>
     <span class="doccomment">/// `(?-u:\xFF)` will cause the parser to return an error, since it would</span>
     <span class="doccomment">/// otherwise match invalid UTF-8. When enabled, it will be allowed.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">allow_bytes</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">yes</span>: <span class="ident">bool</span>) <span class="op">-&gt;</span> <span class="ident">ExprBuilder</span> {
         <span class="self">self</span>.<span class="ident">flags</span>.<span class="ident">allow_bytes</span> <span class="op">=</span> <span class="ident">yes</span>;
         <span class="self">self</span>
     }

     <span class="doccomment">/// Set the nesting limit for regular expression parsing.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// Regular expressions that nest more than this limit will result in a</span>
     <span class="doccomment">/// `StackExhausted` error.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">nest_limit</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">limit</span>: <span class="ident">usize</span>) <span class="op">-&gt;</span> <span class="ident">ExprBuilder</span> {
         <span class="self">self</span>.<span class="ident">nest_limit</span> <span class="op">=</span> <span class="ident">limit</span>;
         <span class="self">self</span>
     }

     <span class="doccomment">/// Parse a string as a regular expression using the current configuraiton.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">parse</span>(<span class="self">self</span>, <span class="ident">s</span>: <span class="kw-2">&amp;</span><span class="ident">str</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">Expr</span><span class="op">&gt;</span> {
         <span class="ident">Parser</span>::<span class="ident">parse</span>(<span class="ident">s</span>, <span class="self">self</span>.<span class="ident">flags</span>).<span class="ident">and_then</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">e</span>.<span class="ident">simplify</span>(<span class="self">self</span>.<span class="ident">nest_limit</span>))
     }
 }

 <span class="kw">impl</span> <span class="ident">Expr</span> {
     <span class="doccomment">/// Parses a string in a regular expression syntax tree.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This is a convenience method for parsing an expression using the</span>
     <span class="doccomment">/// default configuration. To tweak parsing options (such as which flags</span>
     <span class="doccomment">/// are enabled by default), use the `ExprBuilder` type.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">parse</span>(<span class="ident">s</span>: <span class="kw-2">&amp;</span><span class="ident">str</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">Expr</span><span class="op">&gt;</span> {
         <span class="ident">ExprBuilder</span>::<span class="ident">new</span>().<span class="ident">parse</span>(<span class="ident">s</span>)
     }

     <span class="doccomment">/// Returns true iff the expression can be repeated by a quantifier.</span>
     <span class="kw">fn</span> <span class="ident">can_repeat</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">Literal</span>{..} <span class="op">|</span> <span class="ident">LiteralBytes</span>{..}
             <span class="op">|</span> <span class="ident">AnyChar</span> <span class="op">|</span> <span class="ident">AnyCharNoNL</span> <span class="op">|</span> <span class="ident">AnyByte</span> <span class="op">|</span> <span class="ident">AnyByteNoNL</span>
             <span class="op">|</span> <span class="ident">Class</span>(_) <span class="op">|</span> <span class="ident">ClassBytes</span>(_)
             <span class="op">|</span> <span class="ident">StartLine</span> <span class="op">|</span> <span class="ident">EndLine</span> <span class="op">|</span> <span class="ident">StartText</span> <span class="op">|</span> <span class="ident">EndText</span>
             <span class="op">|</span> <span class="ident">WordBoundary</span> <span class="op">|</span> <span class="ident">NotWordBoundary</span>
             <span class="op">|</span> <span class="ident">WordBoundaryAscii</span> <span class="op">|</span> <span class="ident">NotWordBoundaryAscii</span>
             <span class="op">|</span> <span class="ident">Group</span>{..}
             <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             _ <span class="op">=&gt;</span> <span class="bool-val">false</span>,
         }
     }

     <span class="kw">fn</span> <span class="ident">simplify</span>(<span class="self">self</span>, <span class="ident">nest_limit</span>: <span class="ident">usize</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">Expr</span><span class="op">&gt;</span> {
         <span class="kw">fn</span> <span class="ident">combine_literals</span>(<span class="ident">es</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">Expr</span><span class="op">&gt;</span>, <span class="ident">e</span>: <span class="ident">Expr</span>) {
             <span class="kw">match</span> (<span class="ident">es</span>.<span class="ident">pop</span>(), <span class="ident">e</span>) {
                 (<span class="prelude-val">None</span>, <span class="ident">e</span>) <span class="op">=&gt;</span> <span class="ident">es</span>.<span class="ident">push</span>(<span class="ident">e</span>),
                 (<span class="prelude-val">Some</span>(<span class="ident">Literal</span> { <span class="ident">chars</span>: <span class="kw-2">mut</span> <span class="ident">chars1</span>, <span class="ident">casei</span>: <span class="ident">casei1</span> }),
                       <span class="ident">Literal</span> { <span class="ident">chars</span>: <span class="ident">chars2</span>, <span class="ident">casei</span>: <span class="ident">casei2</span> }) <span class="op">=&gt;</span> {
                     <span class="kw">if</span> <span class="ident">casei1</span> <span class="op">==</span> <span class="ident">casei2</span> {
                         <span class="ident">chars1</span>.<span class="ident">extend</span>(<span class="ident">chars2</span>);
                         <span class="ident">es</span>.<span class="ident">push</span>(<span class="ident">Literal</span> { <span class="ident">chars</span>: <span class="ident">chars1</span>, <span class="ident">casei</span>: <span class="ident">casei1</span> });
                     } <span class="kw">else</span> {
                         <span class="ident">es</span>.<span class="ident">push</span>(<span class="ident">Literal</span> { <span class="ident">chars</span>: <span class="ident">chars1</span>, <span class="ident">casei</span>: <span class="ident">casei1</span> });
                         <span class="ident">es</span>.<span class="ident">push</span>(<span class="ident">Literal</span> { <span class="ident">chars</span>: <span class="ident">chars2</span>, <span class="ident">casei</span>: <span class="ident">casei2</span> });
                     }
                 }
                 (<span class="prelude-val">Some</span>(<span class="ident">LiteralBytes</span> { <span class="ident">bytes</span>: <span class="kw-2">mut</span> <span class="ident">bytes1</span>, <span class="ident">casei</span>: <span class="ident">casei1</span> }),
                       <span class="ident">LiteralBytes</span> { <span class="ident">bytes</span>: <span class="ident">bytes2</span>, <span class="ident">casei</span>: <span class="ident">casei2</span> }) <span class="op">=&gt;</span> {
                     <span class="kw">if</span> <span class="ident">casei1</span> <span class="op">==</span> <span class="ident">casei2</span> {
                         <span class="ident">bytes1</span>.<span class="ident">extend</span>(<span class="ident">bytes2</span>);
                         <span class="ident">es</span>.<span class="ident">push</span>(<span class="ident">LiteralBytes</span> { <span class="ident">bytes</span>: <span class="ident">bytes1</span>, <span class="ident">casei</span>: <span class="ident">casei1</span> });
                     } <span class="kw">else</span> {
                         <span class="ident">es</span>.<span class="ident">push</span>(<span class="ident">LiteralBytes</span> { <span class="ident">bytes</span>: <span class="ident">bytes1</span>, <span class="ident">casei</span>: <span class="ident">casei1</span> });
                         <span class="ident">es</span>.<span class="ident">push</span>(<span class="ident">LiteralBytes</span> { <span class="ident">bytes</span>: <span class="ident">bytes2</span>, <span class="ident">casei</span>: <span class="ident">casei2</span> });
                     }
                 }
                 (<span class="prelude-val">Some</span>(<span class="ident">e1</span>), <span class="ident">e2</span>) <span class="op">=&gt;</span> {
                     <span class="ident">es</span>.<span class="ident">push</span>(<span class="ident">e1</span>);
                     <span class="ident">es</span>.<span class="ident">push</span>(<span class="ident">e2</span>);
                 }
             }
         }
         <span class="kw">fn</span> <span class="ident">simp</span>(<span class="ident">expr</span>: <span class="ident">Expr</span>, <span class="ident">recurse</span>: <span class="ident">usize</span>, <span class="ident">limit</span>: <span class="ident">usize</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">Expr</span><span class="op">&gt;</span> {
             <span class="kw">if</span> <span class="ident">recurse</span> <span class="op">&gt;</span> <span class="ident">limit</span> {
                 <span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">Error</span> {
                     <span class="ident">pos</span>: <span class="number">0</span>,
                     <span class="ident">surround</span>: <span class="string">&quot;&quot;</span>.<span class="ident">to_owned</span>(),
                     <span class="ident">kind</span>: <span class="ident">ErrorKind</span>::<span class="ident">StackExhausted</span>,
                 });
             }
             <span class="kw">let</span> <span class="ident">simplify</span> <span class="op">=</span> <span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">simp</span>(<span class="ident">e</span>, <span class="ident">recurse</span> <span class="op">+</span> <span class="number">1</span>, <span class="ident">limit</span>);
             <span class="prelude-val">Ok</span>(<span class="kw">match</span> <span class="ident">expr</span> {
                 <span class="ident">Repeat</span> { <span class="ident">e</span>, <span class="ident">r</span>, <span class="ident">greedy</span> } <span class="op">=&gt;</span> <span class="ident">Repeat</span> {
                     <span class="ident">e</span>: <span class="ident">Box</span>::<span class="ident">new</span>(<span class="macro">try</span><span class="macro">!</span>(<span class="ident">simplify</span>(<span class="kw-2">*</span><span class="ident">e</span>))),
                     <span class="ident">r</span>: <span class="ident">r</span>,
                     <span class="ident">greedy</span>: <span class="ident">greedy</span>,
                 },
                 <span class="ident">Group</span> { <span class="ident">e</span>, <span class="ident">i</span>, <span class="ident">name</span> } <span class="op">=&gt;</span> {
                     <span class="kw">let</span> <span class="ident">e</span> <span class="op">=</span> <span class="macro">try</span><span class="macro">!</span>(<span class="ident">simplify</span>(<span class="kw-2">*</span><span class="ident">e</span>));
                     <span class="kw">if</span> <span class="ident">i</span>.<span class="ident">is_none</span>() <span class="op">&amp;&amp;</span> <span class="ident">name</span>.<span class="ident">is_none</span>() <span class="op">&amp;&amp;</span> <span class="ident">e</span>.<span class="ident">can_repeat</span>() {
                         <span class="ident">e</span>
                     } <span class="kw">else</span> {
                         <span class="ident">Group</span> { <span class="ident">e</span>: <span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">e</span>), <span class="ident">i</span>: <span class="ident">i</span>, <span class="ident">name</span>: <span class="ident">name</span> }
                     }
                 }
                 <span class="ident">Concat</span>(<span class="ident">es</span>) <span class="op">=&gt;</span> {
                     <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">new_es</span> <span class="op">=</span> <span class="ident">Vec</span>::<span class="ident">with_capacity</span>(<span class="ident">es</span>.<span class="ident">len</span>());
                     <span class="kw">for</span> <span class="ident">e</span> <span class="kw">in</span> <span class="ident">es</span> {
                         <span class="ident">combine_literals</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">new_es</span>, <span class="macro">try</span><span class="macro">!</span>(<span class="ident">simplify</span>(<span class="ident">e</span>)));
                     }
                     <span class="kw">if</span> <span class="ident">new_es</span>.<span class="ident">len</span>() <span class="op">==</span> <span class="number">1</span> {
                         <span class="ident">new_es</span>.<span class="ident">pop</span>().<span class="ident">unwrap</span>()
                     } <span class="kw">else</span> {
                         <span class="ident">Concat</span>(<span class="ident">new_es</span>)
                     }
                 }
                 <span class="ident">Alternate</span>(<span class="ident">es</span>) <span class="op">=&gt;</span> {
                     <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">new_es</span> <span class="op">=</span> <span class="ident">Vec</span>::<span class="ident">with_capacity</span>(<span class="ident">es</span>.<span class="ident">len</span>());
                     <span class="kw">for</span> <span class="ident">e</span> <span class="kw">in</span> <span class="ident">es</span> {
                         <span class="ident">new_es</span>.<span class="ident">push</span>(<span class="macro">try</span><span class="macro">!</span>(<span class="ident">simplify</span>(<span class="ident">e</span>)));
                     }
                     <span class="ident">Alternate</span>(<span class="ident">new_es</span>)
                 }
                 <span class="ident">e</span> <span class="op">=&gt;</span> <span class="ident">e</span>,
             })
         }
         <span class="ident">simp</span>(<span class="self">self</span>, <span class="number">0</span>, <span class="ident">nest_limit</span>)
     }

     <span class="doccomment">/// Returns a set of literal prefixes extracted from this expression.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">prefixes</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Literals</span> {
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">lits</span> <span class="op">=</span> <span class="ident">Literals</span>::<span class="ident">empty</span>();
         <span class="ident">lits</span>.<span class="ident">union_prefixes</span>(<span class="self">self</span>);
         <span class="ident">lits</span>
     }

     <span class="doccomment">/// Returns a set of literal suffixes extracted from this expression.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">suffixes</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Literals</span> {
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">lits</span> <span class="op">=</span> <span class="ident">Literals</span>::<span class="ident">empty</span>();
         <span class="ident">lits</span>.<span class="ident">union_suffixes</span>(<span class="self">self</span>);
         <span class="ident">lits</span>
     }

     <span class="doccomment">/// Returns true if and only if the expression is required to match from</span>
     <span class="doccomment">/// the beginning of text.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is_anchored_start</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">Repeat</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, <span class="ident">r</span>, .. } <span class="op">=&gt;</span> {
                 <span class="op">!</span><span class="ident">r</span>.<span class="ident">matches_empty</span>() <span class="op">&amp;&amp;</span> <span class="ident">e</span>.<span class="ident">is_anchored_start</span>()
             }
             <span class="ident">Group</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, .. } <span class="op">=&gt;</span> <span class="ident">e</span>.<span class="ident">is_anchored_start</span>(),
             <span class="ident">Concat</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>[<span class="number">0</span>].<span class="ident">is_anchored_start</span>(),
             <span class="ident">Alternate</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>.<span class="ident">iter</span>().<span class="ident">all</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">e</span>.<span class="ident">is_anchored_start</span>()),
             <span class="ident">StartText</span> <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             _ <span class="op">=&gt;</span> <span class="bool-val">false</span>,
         }
     }

     <span class="doccomment">/// Returns true if and only if the expression has at least one matchable</span>
     <span class="doccomment">/// sub-expression that must match the beginning of text.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">has_anchored_start</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">Repeat</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, <span class="ident">r</span>, .. } <span class="op">=&gt;</span> {
                 <span class="op">!</span><span class="ident">r</span>.<span class="ident">matches_empty</span>() <span class="op">&amp;&amp;</span> <span class="ident">e</span>.<span class="ident">has_anchored_start</span>()
             }
             <span class="ident">Group</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, .. } <span class="op">=&gt;</span> <span class="ident">e</span>.<span class="ident">has_anchored_start</span>(),
             <span class="ident">Concat</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>[<span class="number">0</span>].<span class="ident">has_anchored_start</span>(),
             <span class="ident">Alternate</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>.<span class="ident">iter</span>().<span class="ident">any</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">e</span>.<span class="ident">has_anchored_start</span>()),
             <span class="ident">StartText</span> <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             _ <span class="op">=&gt;</span> <span class="bool-val">false</span>,
         }
     }

     <span class="doccomment">/// Returns true if and only if the expression is required to match at the</span>
     <span class="doccomment">/// end of the text.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is_anchored_end</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">Repeat</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, <span class="ident">r</span>, .. } <span class="op">=&gt;</span> {
                 <span class="op">!</span><span class="ident">r</span>.<span class="ident">matches_empty</span>() <span class="op">&amp;&amp;</span> <span class="ident">e</span>.<span class="ident">is_anchored_end</span>()
             }
             <span class="ident">Group</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, .. } <span class="op">=&gt;</span> <span class="ident">e</span>.<span class="ident">is_anchored_end</span>(),
             <span class="ident">Concat</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>[<span class="ident">es</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="number">1</span>].<span class="ident">is_anchored_end</span>(),
             <span class="ident">Alternate</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>.<span class="ident">iter</span>().<span class="ident">all</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">e</span>.<span class="ident">is_anchored_end</span>()),
             <span class="ident">EndText</span> <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             _ <span class="op">=&gt;</span> <span class="bool-val">false</span>,
         }
     }

     <span class="doccomment">/// Returns true if and only if the expression has at least one matchable</span>
     <span class="doccomment">/// sub-expression that must match the beginning of text.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">has_anchored_end</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">Repeat</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, <span class="ident">r</span>, .. } <span class="op">=&gt;</span> {
                 <span class="op">!</span><span class="ident">r</span>.<span class="ident">matches_empty</span>() <span class="op">&amp;&amp;</span> <span class="ident">e</span>.<span class="ident">has_anchored_end</span>()
             }
             <span class="ident">Group</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, .. } <span class="op">=&gt;</span> <span class="ident">e</span>.<span class="ident">has_anchored_end</span>(),
             <span class="ident">Concat</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>[<span class="ident">es</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="number">1</span>].<span class="ident">has_anchored_end</span>(),
             <span class="ident">Alternate</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>.<span class="ident">iter</span>().<span class="ident">any</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">e</span>.<span class="ident">has_anchored_end</span>()),
             <span class="ident">EndText</span> <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             _ <span class="op">=&gt;</span> <span class="bool-val">false</span>,
         }
     }

     <span class="doccomment">/// Returns true if and only if the expression contains sub-expressions</span>
     <span class="doccomment">/// that can match arbitrary bytes.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">has_bytes</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">Repeat</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, .. } <span class="op">=&gt;</span> <span class="ident">e</span>.<span class="ident">has_bytes</span>(),
             <span class="ident">Group</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, .. } <span class="op">=&gt;</span> <span class="ident">e</span>.<span class="ident">has_bytes</span>(),
             <span class="ident">Concat</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>.<span class="ident">iter</span>().<span class="ident">any</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">e</span>.<span class="ident">has_bytes</span>()),
             <span class="ident">Alternate</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> <span class="ident">es</span>.<span class="ident">iter</span>().<span class="ident">any</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">e</span>.<span class="ident">has_bytes</span>()),
             <span class="ident">LiteralBytes</span>{..} <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             <span class="ident">AnyByte</span> <span class="op">|</span> <span class="ident">AnyByteNoNL</span> <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             <span class="ident">ClassBytes</span>(_) <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             <span class="ident">WordBoundaryAscii</span> <span class="op">|</span> <span class="ident">NotWordBoundaryAscii</span> <span class="op">=&gt;</span> <span class="bool-val">true</span>,
             _ <span class="op">=&gt;</span> <span class="bool-val">false</span>,
         }
     }
 }

 <span class="kw">impl</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">CharClass</span> {
     <span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ClassRange</span><span class="op">&gt;</span>;
     <span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ClassRange</span><span class="op">&gt;</span> { <span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">ranges</span> }
 }

 <span class="kw">impl</span> <span class="ident">IntoIterator</span> <span class="kw">for</span> <span class="ident">CharClass</span> {
     <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">ClassRange</span>;
     <span class="kw">type</span> <span class="ident">IntoIter</span> <span class="op">=</span> <span class="ident">vec</span>::<span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">ClassRange</span><span class="op">&gt;</span>;
     <span class="kw">fn</span> <span class="ident">into_iter</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">vec</span>::<span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">ClassRange</span><span class="op">&gt;</span> { <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">into_iter</span>() }
 }

 <span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">IntoIterator</span> <span class="kw">for</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">CharClass</span> {
     <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">ClassRange</span>;
     <span class="kw">type</span> <span class="ident">IntoIter</span> <span class="op">=</span> <span class="ident">slice</span>::<span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">ClassRange</span><span class="op">&gt;</span>;
     <span class="kw">fn</span> <span class="ident">into_iter</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">slice</span>::<span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">ClassRange</span><span class="op">&gt;</span> { <span class="self">self</span>.<span class="ident">iter</span>() }
 }

 <span class="kw">impl</span> <span class="ident">CharClass</span> {
     <span class="doccomment">/// Create a new class from an existing set of ranges.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">ranges</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ClassRange</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="ident">CharClass</span> {
         <span class="ident">CharClass</span> { <span class="ident">ranges</span>: <span class="ident">ranges</span> }
     }

     <span class="doccomment">/// Create an empty class.</span>
     <span class="kw">fn</span> <span class="ident">empty</span>() <span class="op">-&gt;</span> <span class="ident">CharClass</span> {
         <span class="ident">CharClass</span>::<span class="ident">new</span>(<span class="ident">Vec</span>::<span class="ident">new</span>())
     }

     <span class="doccomment">/// Returns true if `c` is matched by this character class.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">matches</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">c</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="self">self</span>.<span class="ident">binary_search_by</span>(<span class="op">|</span><span class="ident">range</span><span class="op">|</span> <span class="ident">c</span>.<span class="ident">partial_cmp</span>(<span class="ident">range</span>).<span class="ident">unwrap</span>()).<span class="ident">is_ok</span>()
     }

     <span class="doccomment">/// Removes the given character from the class if it exists.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// Note that this takes `O(n)` time in the number of ranges.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">remove</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">c</span>: <span class="ident">char</span>) {
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">i</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">binary_search_by</span>(<span class="op">|</span><span class="ident">r</span><span class="op">|</span> <span class="ident">c</span>.<span class="ident">partial_cmp</span>(<span class="ident">r</span>).<span class="ident">unwrap</span>()) {
             <span class="prelude-val">Ok</span>(<span class="ident">i</span>) <span class="op">=&gt;</span> <span class="ident">i</span>,
             <span class="prelude-val">Err</span>(_) <span class="op">=&gt;</span> <span class="kw">return</span>,
         };
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">r</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">remove</span>(<span class="ident">i</span>);
         <span class="kw">if</span> <span class="ident">r</span>.<span class="ident">start</span> <span class="op">==</span> <span class="ident">c</span> {
             <span class="ident">r</span>.<span class="ident">start</span> <span class="op">=</span> <span class="ident">inc_char</span>(<span class="ident">c</span>);
             <span class="kw">if</span> <span class="ident">r</span>.<span class="ident">start</span> <span class="op">&gt;</span> <span class="ident">r</span>.<span class="ident">end</span> <span class="op">||</span> <span class="ident">c</span> <span class="op">==</span> <span class="ident">char</span>::<span class="ident">MAX</span> {
                 <span class="kw">return</span>;
             }
             <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">insert</span>(<span class="ident">i</span>, <span class="ident">r</span>);
         } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">r</span>.<span class="ident">end</span> <span class="op">==</span> <span class="ident">c</span> {
             <span class="ident">r</span>.<span class="ident">end</span> <span class="op">=</span> <span class="ident">dec_char</span>(<span class="ident">c</span>);
             <span class="kw">if</span> <span class="ident">r</span>.<span class="ident">end</span> <span class="op">&lt;</span> <span class="ident">r</span>.<span class="ident">start</span> <span class="op">||</span> <span class="ident">c</span> <span class="op">==</span> <span class="string">&#39;\x00&#39;</span> {
                 <span class="kw">return</span>;
             }
             <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">insert</span>(<span class="number">0</span>, <span class="ident">r</span>);
         } <span class="kw">else</span> {
             <span class="kw">let</span> (<span class="kw-2">mut</span> <span class="ident">r1</span>, <span class="kw-2">mut</span> <span class="ident">r2</span>) <span class="op">=</span> (<span class="ident">r</span>.<span class="ident">clone</span>(), <span class="ident">r</span>.<span class="ident">clone</span>());
             <span class="ident">r1</span>.<span class="ident">end</span> <span class="op">=</span> <span class="ident">dec_char</span>(<span class="ident">c</span>);
             <span class="kw">if</span> <span class="ident">r1</span>.<span class="ident">start</span> <span class="op">&lt;=</span> <span class="ident">r1</span>.<span class="ident">end</span> {
                 <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">insert</span>(<span class="ident">i</span>, <span class="ident">r1</span>);
                 <span class="ident">i</span> <span class="op">+=</span> <span class="number">1</span>;
             }
             <span class="ident">r2</span>.<span class="ident">start</span> <span class="op">=</span> <span class="ident">inc_char</span>(<span class="ident">c</span>);
             <span class="kw">if</span> <span class="ident">r2</span>.<span class="ident">start</span> <span class="op">&lt;=</span> <span class="ident">r2</span>.<span class="ident">end</span> {
                 <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">insert</span>(<span class="ident">i</span>, <span class="ident">r2</span>);
             }
         }
     }

     <span class="doccomment">/// Create a new empty class from this one.</span>
     <span class="kw">fn</span> <span class="ident">to_empty</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">CharClass</span> {
         <span class="ident">CharClass</span> { <span class="ident">ranges</span>: <span class="ident">Vec</span>::<span class="ident">with_capacity</span>(<span class="self">self</span>.<span class="ident">len</span>()) }
     }

     <span class="doccomment">/// Create a byte class from this character class.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// Codepoints above 0xFF are removed.</span>
     <span class="kw">fn</span> <span class="ident">to_byte_class</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">ByteClass</span> {
         <span class="ident">ByteClass</span>::<span class="ident">new</span>(
             <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">into_iter</span>()
                        .<span class="ident">filter_map</span>(<span class="op">|</span><span class="ident">r</span><span class="op">|</span> <span class="ident">r</span>.<span class="ident">to_byte_range</span>())
                        .<span class="ident">collect</span>()).<span class="ident">canonicalize</span>()
     }

     <span class="doccomment">/// Merge two classes and canonicalize them.</span>
     <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
     <span class="kw">fn</span> <span class="ident">merge</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">other</span>: <span class="ident">CharClass</span>) <span class="op">-&gt;</span> <span class="ident">CharClass</span> {
         <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">extend</span>(<span class="ident">other</span>);
         <span class="self">self</span>.<span class="ident">canonicalize</span>()
     }

     <span class="doccomment">/// Canonicalze any sequence of ranges.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This is responsible for enforcing the canonical format invariants</span>
     <span class="doccomment">/// as described on the docs for the `CharClass` type.</span>
     <span class="kw">fn</span> <span class="ident">canonicalize</span>(<span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">CharClass</span> {
         <span class="comment">// TODO: Save some cycles here by checking if already canonicalized.</span>
         <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">sort</span>();
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ordered</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">to_empty</span>(); <span class="comment">// TODO: Do this in place?</span>
         <span class="kw">for</span> <span class="ident">candidate</span> <span class="kw">in</span> <span class="self">self</span> {
             <span class="comment">// If the candidate overlaps with an existing range, then it must</span>
             <span class="comment">// be the most recent range added because we process the candidates</span>
             <span class="comment">// in order.</span>
             <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">or</span>) <span class="op">=</span> <span class="ident">ordered</span>.<span class="ident">ranges</span>.<span class="ident">last_mut</span>() {
                 <span class="kw">if</span> <span class="ident">or</span>.<span class="ident">overlapping</span>(<span class="ident">candidate</span>) {
                     <span class="kw-2">*</span><span class="ident">or</span> <span class="op">=</span> <span class="ident">or</span>.<span class="ident">merge</span>(<span class="ident">candidate</span>);
                     <span class="kw">continue</span>;
                 }
             }
             <span class="ident">ordered</span>.<span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">candidate</span>);
         }
         <span class="ident">ordered</span>
     }

     <span class="doccomment">/// Negates the character class.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// For all `c` where `c` is a Unicode scalar value, `c` matches `self`</span>
     <span class="doccomment">/// if and only if `c` does not match `self.negate()`.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">negate</span>(<span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">CharClass</span> {
         <span class="kw">fn</span> <span class="ident">range</span>(<span class="ident">s</span>: <span class="ident">char</span>, <span class="ident">e</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">ClassRange</span> { <span class="ident">ClassRange</span>::<span class="ident">new</span>(<span class="ident">s</span>, <span class="ident">e</span>) }

         <span class="kw">if</span> <span class="self">self</span>.<span class="ident">is_empty</span>() {
             <span class="comment">// Inverting an empty range yields all of Unicode.</span>
             <span class="kw">return</span> <span class="ident">CharClass</span> {
                 <span class="ident">ranges</span>: <span class="macro">vec</span><span class="macro">!</span>[<span class="ident">ClassRange</span> { <span class="ident">start</span>: <span class="string">&#39;\x00&#39;</span>, <span class="ident">end</span>: <span class="string">&#39;\u{10ffff}&#39;</span> }],
             };
         }
         <span class="self">self</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">canonicalize</span>();
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">inv</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">to_empty</span>();
         <span class="kw">if</span> <span class="self">self</span>[<span class="number">0</span>].<span class="ident">start</span> <span class="op">&gt;</span> <span class="string">&#39;\x00&#39;</span> {
             <span class="ident">inv</span>.<span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">range</span>(<span class="string">&#39;\x00&#39;</span>, <span class="ident">dec_char</span>(<span class="self">self</span>[<span class="number">0</span>].<span class="ident">start</span>)));
         }
         <span class="kw">for</span> <span class="ident">win</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">windows</span>(<span class="number">2</span>) {
             <span class="ident">inv</span>.<span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">range</span>(<span class="ident">inc_char</span>(<span class="ident">win</span>[<span class="number">0</span>].<span class="ident">end</span>),
                                   <span class="ident">dec_char</span>(<span class="ident">win</span>[<span class="number">1</span>].<span class="ident">start</span>)));
         }
         <span class="kw">if</span> <span class="self">self</span>[<span class="self">self</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="number">1</span>].<span class="ident">end</span> <span class="op">&lt;</span> <span class="ident">char</span>::<span class="ident">MAX</span> {
             <span class="ident">inv</span>.<span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">range</span>(<span class="ident">inc_char</span>(<span class="self">self</span>[<span class="self">self</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="number">1</span>].<span class="ident">end</span>),
                                   <span class="ident">char</span>::<span class="ident">MAX</span>));
         }
         <span class="ident">inv</span>
     }

     <span class="doccomment">/// Apply case folding to this character class.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// N.B. Applying case folding to a negated character class probably</span>
     <span class="doccomment">/// won&#39;t produce the expected result. e.g., `(?i)[^x]` really should</span>
     <span class="doccomment">/// match any character sans `x` and `X`, but if `[^x]` is negated</span>
     <span class="doccomment">/// before being case folded, you&#39;ll end up matching any character.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">case_fold</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">CharClass</span> {
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">folded</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">to_empty</span>();
         <span class="kw">for</span> <span class="ident">r</span> <span class="kw">in</span> <span class="self">self</span> {
             <span class="comment">// Applying case folding to a range is expensive because *every*</span>
             <span class="comment">// character needs to be examined. Thus, we avoid that drudgery</span>
             <span class="comment">// if no character in the current range is in our case folding</span>
             <span class="comment">// table.</span>
             <span class="kw">if</span> <span class="ident">r</span>.<span class="ident">needs_case_folding</span>() {
                 <span class="ident">folded</span>.<span class="ident">ranges</span>.<span class="ident">extend</span>(<span class="ident">r</span>.<span class="ident">case_fold</span>());
             }
             <span class="ident">folded</span>.<span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">r</span>);
         }
         <span class="ident">folded</span>.<span class="ident">canonicalize</span>()
     }

     <span class="doccomment">/// Returns the number of characters that match this class.</span>
     <span class="kw">fn</span> <span class="ident">num_chars</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
         <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">iter</span>()
             .<span class="ident">map</span>(<span class="op">|</span><span class="kw-2">&amp;</span><span class="ident">r</span><span class="op">|</span> <span class="number">1</span> <span class="op">+</span> (<span class="ident">r</span>.<span class="ident">end</span> <span class="kw">as</span> <span class="ident">u32</span>) <span class="op">-</span> (<span class="ident">r</span>.<span class="ident">start</span> <span class="kw">as</span> <span class="ident">u32</span>))
             .<span class="ident">fold</span>(<span class="number">0</span>, <span class="op">|</span><span class="ident">acc</span>, <span class="ident">len</span><span class="op">|</span> <span class="ident">acc</span> <span class="op">+</span> <span class="ident">len</span>)
             <span class="kw">as</span> <span class="ident">usize</span>
     }
 }

 <span class="kw">impl</span> <span class="ident">ClassRange</span> {
     <span class="doccomment">/// Create a new class range.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// If `end &lt; start`, then the two values are swapped so that</span>
     <span class="doccomment">/// the invariant `start &lt;= end` is preserved.</span>
     <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">start</span>: <span class="ident">char</span>, <span class="ident">end</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">ClassRange</span> {
         <span class="kw">if</span> <span class="ident">start</span> <span class="op">&lt;=</span> <span class="ident">end</span> {
             <span class="ident">ClassRange</span> { <span class="ident">start</span>: <span class="ident">start</span>, <span class="ident">end</span>: <span class="ident">end</span> }
         } <span class="kw">else</span> {
             <span class="ident">ClassRange</span> { <span class="ident">start</span>: <span class="ident">end</span>, <span class="ident">end</span>: <span class="ident">start</span> }
         }
     }

     <span class="doccomment">/// Translate this to a byte class.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// If the start codepoint exceeds 0xFF, then this returns `None`.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// If the end codepoint exceeds 0xFF, then it is set to 0xFF.</span>
     <span class="kw">fn</span> <span class="ident">to_byte_range</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span> {
         <span class="kw">if</span> <span class="self">self</span>.<span class="ident">start</span> <span class="op">&gt;</span> <span class="string">&#39;\u{FF}&#39;</span> {
             <span class="prelude-val">None</span>
         } <span class="kw">else</span> {
             <span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">start</span> <span class="kw">as</span> <span class="ident">u8</span>;
             <span class="kw">let</span> <span class="ident">e</span> <span class="op">=</span> <span class="ident">min</span>(<span class="string">&#39;\u{FF}&#39;</span>, <span class="self">self</span>.<span class="ident">end</span>) <span class="kw">as</span> <span class="ident">u8</span>;
             <span class="prelude-val">Some</span>(<span class="ident">ByteRange</span>::<span class="ident">new</span>(<span class="ident">s</span>, <span class="ident">e</span>))
         }
     }

     <span class="doccomment">/// Create a range of one character.</span>
     <span class="kw">fn</span> <span class="ident">one</span>(<span class="ident">c</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">ClassRange</span> {
         <span class="ident">ClassRange</span> { <span class="ident">start</span>: <span class="ident">c</span>, <span class="ident">end</span>: <span class="ident">c</span> }
     }

     <span class="doccomment">/// Returns true if and only if the two ranges are overlapping. Note that</span>
     <span class="doccomment">/// since ranges are inclusive, `a-c` and `d-f` are overlapping!</span>
     <span class="kw">fn</span> <span class="ident">overlapping</span>(<span class="self">self</span>, <span class="ident">other</span>: <span class="ident">ClassRange</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="ident">max</span>(<span class="self">self</span>.<span class="ident">start</span>, <span class="ident">other</span>.<span class="ident">start</span>) <span class="op">&lt;=</span> <span class="ident">inc_char</span>(<span class="ident">min</span>(<span class="self">self</span>.<span class="ident">end</span>, <span class="ident">other</span>.<span class="ident">end</span>))
     }

     <span class="doccomment">/// Creates a new range representing the union of `self` and `other.</span>
     <span class="kw">fn</span> <span class="ident">merge</span>(<span class="self">self</span>, <span class="ident">other</span>: <span class="ident">ClassRange</span>) <span class="op">-&gt;</span> <span class="ident">ClassRange</span> {
         <span class="ident">ClassRange</span> {
             <span class="ident">start</span>: <span class="ident">min</span>(<span class="self">self</span>.<span class="ident">start</span>, <span class="ident">other</span>.<span class="ident">start</span>),
             <span class="ident">end</span>: <span class="ident">max</span>(<span class="self">self</span>.<span class="ident">end</span>, <span class="ident">other</span>.<span class="ident">end</span>),
         }
     }

     <span class="doccomment">/// Returns true if and only if this range contains a character that is</span>
     <span class="doccomment">/// in the case folding table.</span>
     <span class="kw">fn</span> <span class="ident">needs_case_folding</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="ident">case_folding</span>::<span class="ident">C_plus_S_both_table</span>
         .<span class="ident">binary_search_by</span>(<span class="op">|</span><span class="kw-2">&amp;</span>(<span class="ident">c</span>, _)<span class="op">|</span> <span class="self">self</span>.<span class="ident">partial_cmp</span>(<span class="kw-2">&amp;</span><span class="ident">c</span>).<span class="ident">unwrap</span>()).<span class="ident">is_ok</span>()
     }

     <span class="doccomment">/// Apply case folding to this range.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// Since case folding might add characters such that the range is no</span>
     <span class="doccomment">/// longer contiguous, this returns multiple class ranges. They are in</span>
     <span class="doccomment">/// canonical order.</span>
     <span class="kw">fn</span> <span class="ident">case_fold</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ClassRange</span><span class="op">&gt;</span> {
         <span class="kw">let</span> <span class="ident">table</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="ident">case_folding</span>::<span class="ident">C_plus_S_both_table</span>;
         <span class="kw">let</span> (<span class="ident">s</span>, <span class="ident">e</span>) <span class="op">=</span> (<span class="self">self</span>.<span class="ident">start</span> <span class="kw">as</span> <span class="ident">u32</span>, <span class="self">self</span>.<span class="ident">end</span> <span class="kw">as</span> <span class="ident">u32</span> <span class="op">+</span> <span class="number">1</span>);
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">start</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">start</span>;
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">end</span> <span class="op">=</span> <span class="ident">start</span>;
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">next_case_fold</span> <span class="op">=</span> <span class="string">&#39;\x00&#39;</span>;
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ranges</span> <span class="op">=</span> <span class="ident">Vec</span>::<span class="ident">with_capacity</span>(<span class="number">10</span>);
         <span class="kw">for</span> <span class="kw-2">mut</span> <span class="ident">c</span> <span class="kw">in</span> (<span class="ident">s</span>..<span class="ident">e</span>).<span class="ident">filter_map</span>(<span class="ident">char</span>::<span class="ident">from_u32</span>) {
             <span class="kw">if</span> <span class="ident">c</span> <span class="op">&gt;=</span> <span class="ident">next_case_fold</span> {
                 <span class="ident">c</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">simple_case_fold_both_result</span>(<span class="ident">c</span>) {
                     <span class="prelude-val">Ok</span>(<span class="ident">i</span>) <span class="op">=&gt;</span> {
                         <span class="kw">for</span> <span class="kw-2">&amp;</span>(<span class="ident">c1</span>, <span class="ident">c2</span>) <span class="kw">in</span> <span class="kw-2">&amp;</span><span class="ident">table</span>[<span class="ident">i</span>..] {
                             <span class="kw">if</span> <span class="ident">c1</span> <span class="op">!=</span> <span class="ident">c</span> {
                                 <span class="kw">break</span>;
                             }
                             <span class="kw">if</span> <span class="ident">c2</span> <span class="op">!=</span> <span class="ident">inc_char</span>(<span class="ident">end</span>) {
                                 <span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">ClassRange</span>::<span class="ident">new</span>(<span class="ident">start</span>, <span class="ident">end</span>));
                                 <span class="ident">start</span> <span class="op">=</span> <span class="ident">c2</span>;
                             }
                             <span class="ident">end</span> <span class="op">=</span> <span class="ident">c2</span>;
                         }
                         <span class="kw">continue</span>;
                     }
                     <span class="prelude-val">Err</span>(<span class="ident">i</span>) <span class="op">=&gt;</span> {
                         <span class="kw">if</span> <span class="ident">i</span> <span class="op">&lt;</span> <span class="ident">table</span>.<span class="ident">len</span>() {
                             <span class="ident">next_case_fold</span> <span class="op">=</span> <span class="ident">table</span>[<span class="ident">i</span>].<span class="number">0</span>;
                         } <span class="kw">else</span> {
                             <span class="ident">next_case_fold</span> <span class="op">=</span> <span class="string">&#39;\u{10FFFF}&#39;</span>;
                         }
                         <span class="ident">c</span>
                     }
                 };
             }
             <span class="comment">// The fast path. We know this character doesn&#39;t have an entry</span>
             <span class="comment">// in the case folding table.</span>
             <span class="kw">if</span> <span class="ident">c</span> <span class="op">!=</span> <span class="ident">inc_char</span>(<span class="ident">end</span>) {
                 <span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">ClassRange</span>::<span class="ident">new</span>(<span class="ident">start</span>, <span class="ident">end</span>));
                 <span class="ident">start</span> <span class="op">=</span> <span class="ident">c</span>;
             }
             <span class="ident">end</span> <span class="op">=</span> <span class="ident">c</span>;
         }
         <span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">ClassRange</span>::<span class="ident">new</span>(<span class="ident">start</span>, <span class="ident">end</span>));
         <span class="ident">ranges</span>
     }
 }

 <span class="kw">impl</span> <span class="ident">PartialEq</span><span class="op">&lt;</span><span class="ident">char</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">ClassRange</span> {
     <span class="attribute">#[<span class="ident">inline</span>]</span>
     <span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="self">self</span>.<span class="ident">start</span> <span class="op">&lt;=</span> <span class="kw-2">*</span><span class="ident">other</span> <span class="op">&amp;&amp;</span> <span class="kw-2">*</span><span class="ident">other</span> <span class="op">&lt;=</span> <span class="self">self</span>.<span class="ident">end</span>
     }
 }

 <span class="kw">impl</span> <span class="ident">PartialEq</span><span class="op">&lt;</span><span class="ident">ClassRange</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">char</span> {
     <span class="attribute">#[<span class="ident">inline</span>]</span>
     <span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">ClassRange</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="ident">other</span>.<span class="ident">eq</span>(<span class="self">self</span>)
     }
 }

 <span class="kw">impl</span> <span class="ident">PartialOrd</span><span class="op">&lt;</span><span class="ident">char</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">ClassRange</span> {
     <span class="attribute">#[<span class="ident">inline</span>]</span>
     <span class="kw">fn</span> <span class="ident">partial_cmp</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">char</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">Ordering</span><span class="op">&gt;</span> {
         <span class="prelude-val">Some</span>(<span class="kw">if</span> <span class="self">self</span> <span class="op">==</span> <span class="ident">other</span> {
             <span class="ident">Ordering</span>::<span class="ident">Equal</span>
         } <span class="kw">else</span> <span class="kw">if</span> <span class="kw-2">*</span><span class="ident">other</span> <span class="op">&gt;</span> <span class="self">self</span>.<span class="ident">end</span> {
             <span class="ident">Ordering</span>::<span class="ident">Greater</span>
         } <span class="kw">else</span> {
             <span class="ident">Ordering</span>::<span class="ident">Less</span>
         })
     }
 }

 <span class="kw">impl</span> <span class="ident">PartialOrd</span><span class="op">&lt;</span><span class="ident">ClassRange</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">char</span> {
     <span class="attribute">#[<span class="ident">inline</span>]</span>
     <span class="kw">fn</span> <span class="ident">partial_cmp</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">ClassRange</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">Ordering</span><span class="op">&gt;</span> {
         <span class="ident">other</span>.<span class="ident">partial_cmp</span>(<span class="self">self</span>).<span class="ident">map</span>(<span class="op">|</span><span class="ident">o</span><span class="op">|</span> <span class="ident">o</span>.<span class="ident">reverse</span>())
     }
 }

 <span class="kw">impl</span> <span class="ident">ByteClass</span> {
     <span class="doccomment">/// Create a new class from an existing set of ranges.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">ranges</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="ident">ByteClass</span> {
         <span class="ident">ByteClass</span> { <span class="ident">ranges</span>: <span class="ident">ranges</span> }
     }

     <span class="doccomment">/// Returns true if `b` is matched by this byte class.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">matches</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">b</span>: <span class="ident">u8</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="self">self</span>.<span class="ident">binary_search_by</span>(<span class="op">|</span><span class="ident">range</span><span class="op">|</span> <span class="ident">b</span>.<span class="ident">partial_cmp</span>(<span class="ident">range</span>).<span class="ident">unwrap</span>()).<span class="ident">is_ok</span>()
     }

     <span class="doccomment">/// Removes the given byte from the class if it exists.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// Note that this takes `O(n)` time in the number of ranges.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">remove</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">b</span>: <span class="ident">u8</span>) {
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">i</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">binary_search_by</span>(<span class="op">|</span><span class="ident">r</span><span class="op">|</span> <span class="ident">b</span>.<span class="ident">partial_cmp</span>(<span class="ident">r</span>).<span class="ident">unwrap</span>()) {
             <span class="prelude-val">Ok</span>(<span class="ident">i</span>) <span class="op">=&gt;</span> <span class="ident">i</span>,
             <span class="prelude-val">Err</span>(_) <span class="op">=&gt;</span> <span class="kw">return</span>,
         };
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">r</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">remove</span>(<span class="ident">i</span>);
         <span class="kw">if</span> <span class="ident">r</span>.<span class="ident">start</span> <span class="op">==</span> <span class="ident">b</span> {
             <span class="ident">r</span>.<span class="ident">start</span> <span class="op">=</span> <span class="ident">b</span>.<span class="ident">saturating_add</span>(<span class="number">1</span>);
             <span class="kw">if</span> <span class="ident">r</span>.<span class="ident">start</span> <span class="op">&gt;</span> <span class="ident">r</span>.<span class="ident">end</span> <span class="op">||</span> <span class="ident">b</span> <span class="op">==</span> <span class="ident">u8</span>::<span class="ident">MAX</span> {
                 <span class="kw">return</span>;
             }
             <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">insert</span>(<span class="ident">i</span>, <span class="ident">r</span>);
         } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">r</span>.<span class="ident">end</span> <span class="op">==</span> <span class="ident">b</span> {
             <span class="ident">r</span>.<span class="ident">end</span> <span class="op">=</span> <span class="ident">b</span>.<span class="ident">saturating_sub</span>(<span class="number">1</span>);
             <span class="kw">if</span> <span class="ident">r</span>.<span class="ident">end</span> <span class="op">&lt;</span> <span class="ident">r</span>.<span class="ident">start</span> <span class="op">||</span> <span class="ident">b</span> <span class="op">==</span> <span class="string">b&#39;\x00&#39;</span> {
                 <span class="kw">return</span>;
             }
             <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">insert</span>(<span class="number">0</span>, <span class="ident">r</span>);
         } <span class="kw">else</span> {
             <span class="kw">let</span> (<span class="kw-2">mut</span> <span class="ident">r1</span>, <span class="kw-2">mut</span> <span class="ident">r2</span>) <span class="op">=</span> (<span class="ident">r</span>.<span class="ident">clone</span>(), <span class="ident">r</span>.<span class="ident">clone</span>());
             <span class="ident">r1</span>.<span class="ident">end</span> <span class="op">=</span> <span class="ident">b</span>.<span class="ident">saturating_sub</span>(<span class="number">1</span>);
             <span class="kw">if</span> <span class="ident">r1</span>.<span class="ident">start</span> <span class="op">&lt;=</span> <span class="ident">r1</span>.<span class="ident">end</span> {
                 <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">insert</span>(<span class="ident">i</span>, <span class="ident">r1</span>);
                 <span class="ident">i</span> <span class="op">+=</span> <span class="number">1</span>;
             }
             <span class="ident">r2</span>.<span class="ident">start</span> <span class="op">=</span> <span class="ident">b</span>.<span class="ident">saturating_add</span>(<span class="number">1</span>);
             <span class="kw">if</span> <span class="ident">r2</span>.<span class="ident">start</span> <span class="op">&lt;=</span> <span class="ident">r2</span>.<span class="ident">end</span> {
                 <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">insert</span>(<span class="ident">i</span>, <span class="ident">r2</span>);
             }
         }
     }

     <span class="doccomment">/// Create a new empty class from this one.</span>
     <span class="kw">fn</span> <span class="ident">to_empty</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">ByteClass</span> {
         <span class="ident">ByteClass</span> { <span class="ident">ranges</span>: <span class="ident">Vec</span>::<span class="ident">with_capacity</span>(<span class="self">self</span>.<span class="ident">len</span>()) }
     }

     <span class="doccomment">/// Canonicalze any sequence of ranges.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This is responsible for enforcing the canonical format invariants</span>
     <span class="doccomment">/// as described on the docs for the `ByteClass` type.</span>
     <span class="kw">fn</span> <span class="ident">canonicalize</span>(<span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">ByteClass</span> {
         <span class="comment">// TODO: Save some cycles here by checking if already canonicalized.</span>
         <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">sort</span>();
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ordered</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">to_empty</span>(); <span class="comment">// TODO: Do this in place?</span>
         <span class="kw">for</span> <span class="ident">candidate</span> <span class="kw">in</span> <span class="self">self</span> {
             <span class="comment">// If the candidate overlaps with an existing range, then it must</span>
             <span class="comment">// be the most recent range added because we process the candidates</span>
             <span class="comment">// in order.</span>
             <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">or</span>) <span class="op">=</span> <span class="ident">ordered</span>.<span class="ident">ranges</span>.<span class="ident">last_mut</span>() {
                 <span class="kw">if</span> <span class="ident">or</span>.<span class="ident">overlapping</span>(<span class="ident">candidate</span>) {
                     <span class="kw-2">*</span><span class="ident">or</span> <span class="op">=</span> <span class="ident">or</span>.<span class="ident">merge</span>(<span class="ident">candidate</span>);
                     <span class="kw">continue</span>;
                 }
             }
             <span class="ident">ordered</span>.<span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">candidate</span>);
         }
         <span class="ident">ordered</span>
     }

     <span class="doccomment">/// Negates the byte class.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// For all `b` where `b` is a byte, `b` matches `self` if and only if `b`</span>
     <span class="doccomment">/// does not match `self.negate()`.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">negate</span>(<span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">ByteClass</span> {
         <span class="kw">fn</span> <span class="ident">range</span>(<span class="ident">s</span>: <span class="ident">u8</span>, <span class="ident">e</span>: <span class="ident">u8</span>) <span class="op">-&gt;</span> <span class="ident">ByteRange</span> { <span class="ident">ByteRange</span>::<span class="ident">new</span>(<span class="ident">s</span>, <span class="ident">e</span>) }

         <span class="kw">if</span> <span class="self">self</span>.<span class="ident">is_empty</span>() {
             <span class="comment">// Inverting an empty range yields all bytes.</span>
             <span class="kw">return</span> <span class="ident">ByteClass</span> {
                 <span class="ident">ranges</span>: <span class="macro">vec</span><span class="macro">!</span>[<span class="ident">ByteRange</span> { <span class="ident">start</span>: <span class="string">b&#39;\x00&#39;</span>, <span class="ident">end</span>: <span class="string">b&#39;\xff&#39;</span> }],
             };
         }
         <span class="self">self</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">canonicalize</span>();
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">inv</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">to_empty</span>();
         <span class="kw">if</span> <span class="self">self</span>[<span class="number">0</span>].<span class="ident">start</span> <span class="op">&gt;</span> <span class="string">b&#39;\x00&#39;</span> {
             <span class="ident">inv</span>.<span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">range</span>(<span class="string">b&#39;\x00&#39;</span>, <span class="self">self</span>[<span class="number">0</span>].<span class="ident">start</span>.<span class="ident">saturating_sub</span>(<span class="number">1</span>)));
         }
         <span class="kw">for</span> <span class="ident">win</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">windows</span>(<span class="number">2</span>) {
             <span class="ident">inv</span>.<span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">range</span>(<span class="ident">win</span>[<span class="number">0</span>].<span class="ident">end</span>.<span class="ident">saturating_add</span>(<span class="number">1</span>),
                                   <span class="ident">win</span>[<span class="number">1</span>].<span class="ident">start</span>.<span class="ident">saturating_sub</span>(<span class="number">1</span>)));
         }
         <span class="kw">if</span> <span class="self">self</span>[<span class="self">self</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="number">1</span>].<span class="ident">end</span> <span class="op">&lt;</span> <span class="ident">u8</span>::<span class="ident">MAX</span> {
             <span class="ident">inv</span>.<span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">range</span>(<span class="self">self</span>[<span class="self">self</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="number">1</span>].<span class="ident">end</span>.<span class="ident">saturating_add</span>(<span class="number">1</span>),
                                   <span class="ident">u8</span>::<span class="ident">MAX</span>));
         }
         <span class="ident">inv</span>
     }

     <span class="doccomment">/// Apply case folding to this byte class.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This assumes that the bytes in the ranges are ASCII compatible.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// N.B. Applying case folding to a negated character class probably</span>
     <span class="doccomment">/// won&#39;t produce the expected result. e.g., `(?i)[^x]` really should</span>
     <span class="doccomment">/// match any character sans `x` and `X`, but if `[^x]` is negated</span>
     <span class="doccomment">/// before being case folded, you&#39;ll end up matching any character.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">case_fold</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">ByteClass</span> {
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">folded</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">to_empty</span>();
         <span class="kw">for</span> <span class="ident">r</span> <span class="kw">in</span> <span class="self">self</span> {
             <span class="ident">folded</span>.<span class="ident">ranges</span>.<span class="ident">extend</span>(<span class="ident">r</span>.<span class="ident">case_fold</span>());
         }
         <span class="ident">folded</span>.<span class="ident">canonicalize</span>()
     }

     <span class="doccomment">/// Returns the number of bytes that match this class.</span>
     <span class="kw">fn</span> <span class="ident">num_bytes</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
         <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">iter</span>()
             .<span class="ident">map</span>(<span class="op">|</span><span class="kw-2">&amp;</span><span class="ident">r</span><span class="op">|</span> <span class="number">1</span> <span class="op">+</span> (<span class="ident">r</span>.<span class="ident">end</span> <span class="kw">as</span> <span class="ident">u32</span>) <span class="op">-</span> (<span class="ident">r</span>.<span class="ident">start</span> <span class="kw">as</span> <span class="ident">u32</span>))
             .<span class="ident">fold</span>(<span class="number">0</span>, <span class="op">|</span><span class="ident">acc</span>, <span class="ident">len</span><span class="op">|</span> <span class="ident">acc</span> <span class="op">+</span> <span class="ident">len</span>)
             <span class="kw">as</span> <span class="ident">usize</span>
     }
 }

 <span class="kw">impl</span> <span class="ident">ByteRange</span> {
     <span class="doccomment">/// Create a new class range.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// If `end &lt; start`, then the two values are swapped so that</span>
     <span class="doccomment">/// the invariant `start &lt;= end` is preserved.</span>
     <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">start</span>: <span class="ident">u8</span>, <span class="ident">end</span>: <span class="ident">u8</span>) <span class="op">-&gt;</span> <span class="ident">ByteRange</span> {
         <span class="kw">if</span> <span class="ident">start</span> <span class="op">&lt;=</span> <span class="ident">end</span> {
             <span class="ident">ByteRange</span> { <span class="ident">start</span>: <span class="ident">start</span>, <span class="ident">end</span>: <span class="ident">end</span> }
         } <span class="kw">else</span> {
             <span class="ident">ByteRange</span> { <span class="ident">start</span>: <span class="ident">end</span>, <span class="ident">end</span>: <span class="ident">start</span> }
         }
     }

     <span class="doccomment">/// Returns true if and only if the two ranges are overlapping. Note that</span>
     <span class="doccomment">/// since ranges are inclusive, `a-c` and `d-f` are overlapping!</span>
     <span class="kw">fn</span> <span class="ident">overlapping</span>(<span class="self">self</span>, <span class="ident">other</span>: <span class="ident">ByteRange</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="ident">max</span>(<span class="self">self</span>.<span class="ident">start</span>, <span class="ident">other</span>.<span class="ident">start</span>)
         <span class="op">&lt;=</span> <span class="ident">min</span>(<span class="self">self</span>.<span class="ident">end</span>, <span class="ident">other</span>.<span class="ident">end</span>).<span class="ident">saturating_add</span>(<span class="number">1</span>)
     }

     <span class="doccomment">/// Returns true if and only if the intersection of self and other is non</span>
     <span class="doccomment">/// empty.</span>
     <span class="kw">fn</span> <span class="ident">is_intersect_empty</span>(<span class="self">self</span>, <span class="ident">other</span>: <span class="ident">ByteRange</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="ident">max</span>(<span class="self">self</span>.<span class="ident">start</span>, <span class="ident">other</span>.<span class="ident">start</span>) <span class="op">&gt;</span> <span class="ident">min</span>(<span class="self">self</span>.<span class="ident">end</span>, <span class="ident">other</span>.<span class="ident">end</span>)
     }

     <span class="doccomment">/// Creates a new range representing the union of `self` and `other.</span>
     <span class="kw">fn</span> <span class="ident">merge</span>(<span class="self">self</span>, <span class="ident">other</span>: <span class="ident">ByteRange</span>) <span class="op">-&gt;</span> <span class="ident">ByteRange</span> {
         <span class="ident">ByteRange</span> {
             <span class="ident">start</span>: <span class="ident">min</span>(<span class="self">self</span>.<span class="ident">start</span>, <span class="ident">other</span>.<span class="ident">start</span>),
             <span class="ident">end</span>: <span class="ident">max</span>(<span class="self">self</span>.<span class="ident">end</span>, <span class="ident">other</span>.<span class="ident">end</span>),
         }
     }

     <span class="doccomment">/// Apply case folding to this range.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// Since case folding might add bytes such that the range is no</span>
     <span class="doccomment">/// longer contiguous, this returns multiple byte ranges.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This assumes that the bytes in this range are ASCII compatible.</span>
     <span class="kw">fn</span> <span class="ident">case_fold</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span> {
         <span class="comment">// So much easier than Unicode case folding!</span>
         <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ranges</span> <span class="op">=</span> <span class="macro">vec</span><span class="macro">!</span>[<span class="self">self</span>];
         <span class="kw">if</span> <span class="op">!</span><span class="ident">ByteRange</span>::<span class="ident">new</span>(<span class="string">b&#39;a&#39;</span>, <span class="string">b&#39;z&#39;</span>).<span class="ident">is_intersect_empty</span>(<span class="self">self</span>) {
             <span class="kw">let</span> <span class="ident">lower</span> <span class="op">=</span> <span class="ident">max</span>(<span class="self">self</span>.<span class="ident">start</span>, <span class="string">b&#39;a&#39;</span>);
             <span class="kw">let</span> <span class="ident">upper</span> <span class="op">=</span> <span class="ident">min</span>(<span class="self">self</span>.<span class="ident">end</span>, <span class="string">b&#39;z&#39;</span>);
             <span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">ByteRange</span>::<span class="ident">new</span>(<span class="ident">lower</span> <span class="op">-</span> <span class="number">32</span>, <span class="ident">upper</span> <span class="op">-</span> <span class="number">32</span>));
         }
         <span class="kw">if</span> <span class="op">!</span><span class="ident">ByteRange</span>::<span class="ident">new</span>(<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;Z&#39;</span>).<span class="ident">is_intersect_empty</span>(<span class="self">self</span>) {
             <span class="kw">let</span> <span class="ident">lower</span> <span class="op">=</span> <span class="ident">max</span>(<span class="self">self</span>.<span class="ident">start</span>, <span class="string">b&#39;A&#39;</span>);
             <span class="kw">let</span> <span class="ident">upper</span> <span class="op">=</span> <span class="ident">min</span>(<span class="self">self</span>.<span class="ident">end</span>, <span class="string">b&#39;Z&#39;</span>);
             <span class="ident">ranges</span>.<span class="ident">push</span>(<span class="ident">ByteRange</span>::<span class="ident">new</span>(<span class="ident">lower</span> <span class="op">+</span> <span class="number">32</span>, <span class="ident">upper</span> <span class="op">+</span> <span class="number">32</span>));
         }
         <span class="ident">ranges</span>
     }
 }

 <span class="kw">impl</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">ByteClass</span> {
     <span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span>;
     <span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span> { <span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">ranges</span> }
 }

 <span class="kw">impl</span> <span class="ident">IntoIterator</span> <span class="kw">for</span> <span class="ident">ByteClass</span> {
     <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">ByteRange</span>;
     <span class="kw">type</span> <span class="ident">IntoIter</span> <span class="op">=</span> <span class="ident">vec</span>::<span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span>;
     <span class="kw">fn</span> <span class="ident">into_iter</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">vec</span>::<span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span> { <span class="self">self</span>.<span class="ident">ranges</span>.<span class="ident">into_iter</span>() }
 }

 <span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">IntoIterator</span> <span class="kw">for</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">ByteClass</span> {
     <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">ByteRange</span>;
     <span class="kw">type</span> <span class="ident">IntoIter</span> <span class="op">=</span> <span class="ident">slice</span>::<span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">ByteRange</span><span class="op">&gt;</span>;
     <span class="kw">fn</span> <span class="ident">into_iter</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">slice</span>::<span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">ByteRange</span><span class="op">&gt;</span> { <span class="self">self</span>.<span class="ident">iter</span>() }
 }

 <span class="kw">impl</span> <span class="ident">PartialEq</span><span class="op">&lt;</span><span class="ident">u8</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">ByteRange</span> {
     <span class="attribute">#[<span class="ident">inline</span>]</span>
     <span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">u8</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="self">self</span>.<span class="ident">start</span> <span class="op">&lt;=</span> <span class="kw-2">*</span><span class="ident">other</span> <span class="op">&amp;&amp;</span> <span class="kw-2">*</span><span class="ident">other</span> <span class="op">&lt;=</span> <span class="self">self</span>.<span class="ident">end</span>
     }
 }

 <span class="kw">impl</span> <span class="ident">PartialEq</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">u8</span> {
     <span class="attribute">#[<span class="ident">inline</span>]</span>
     <span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">ByteRange</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
         <span class="ident">other</span>.<span class="ident">eq</span>(<span class="self">self</span>)
     }
 }

 <span class="kw">impl</span> <span class="ident">PartialOrd</span><span class="op">&lt;</span><span class="ident">u8</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">ByteRange</span> {
     <span class="attribute">#[<span class="ident">inline</span>]</span>
     <span class="kw">fn</span> <span class="ident">partial_cmp</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">u8</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">Ordering</span><span class="op">&gt;</span> {
         <span class="prelude-val">Some</span>(<span class="kw">if</span> <span class="self">self</span> <span class="op">==</span> <span class="ident">other</span> {
             <span class="ident">Ordering</span>::<span class="ident">Equal</span>
         } <span class="kw">else</span> <span class="kw">if</span> <span class="kw-2">*</span><span class="ident">other</span> <span class="op">&gt;</span> <span class="self">self</span>.<span class="ident">end</span> {
             <span class="ident">Ordering</span>::<span class="ident">Greater</span>
         } <span class="kw">else</span> {
             <span class="ident">Ordering</span>::<span class="ident">Less</span>
         })
     }
 }

 <span class="kw">impl</span> <span class="ident">PartialOrd</span><span class="op">&lt;</span><span class="ident">ByteRange</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">u8</span> {
     <span class="attribute">#[<span class="ident">inline</span>]</span>
     <span class="kw">fn</span> <span class="ident">partial_cmp</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">ByteRange</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">Ordering</span><span class="op">&gt;</span> {
         <span class="ident">other</span>.<span class="ident">partial_cmp</span>(<span class="self">self</span>).<span class="ident">map</span>(<span class="op">|</span><span class="ident">o</span><span class="op">|</span> <span class="ident">o</span>.<span class="ident">reverse</span>())
     }
 }

 <span class="doccomment">/// This implementation of `Display` will write a regular expression from the</span>
 <span class="doccomment">/// syntax tree. It does not write the original string parsed.</span>
 <span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">Expr</span> {
     <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">Empty</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;&quot;</span>),
             <span class="ident">Literal</span> { <span class="kw-2">ref</span> <span class="ident">chars</span>, <span class="ident">casei</span> } <span class="op">=&gt;</span> {
                 <span class="kw">if</span> <span class="ident">casei</span> {
                     <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?iu:&quot;</span>));
                 } <span class="kw">else</span> {
                     <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?u:&quot;</span>));
                 }
                 <span class="kw">for</span> <span class="kw-2">&amp;</span><span class="ident">c</span> <span class="kw">in</span> <span class="ident">chars</span> {
                     <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}&quot;</span>, <span class="ident">quote_char</span>(<span class="ident">c</span>)));
                 }
                 <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;)&quot;</span>));
                 <span class="prelude-val">Ok</span>(())
             }
             <span class="ident">LiteralBytes</span> { <span class="kw-2">ref</span> <span class="ident">bytes</span>, <span class="ident">casei</span> } <span class="op">=&gt;</span> {
                 <span class="kw">if</span> <span class="ident">casei</span> {
                     <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?i-u:&quot;</span>));
                 } <span class="kw">else</span> {
                     <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?-u:&quot;</span>));
                 }
                 <span class="kw">for</span> <span class="kw-2">&amp;</span><span class="ident">b</span> <span class="kw">in</span> <span class="ident">bytes</span> {
                     <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}&quot;</span>, <span class="ident">quote_byte</span>(<span class="ident">b</span>)));
                 }
                 <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;)&quot;</span>));
                 <span class="prelude-val">Ok</span>(())
             }
             <span class="ident">AnyChar</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?su:.)&quot;</span>),
             <span class="ident">AnyCharNoNL</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?u:.)&quot;</span>),
             <span class="ident">AnyByte</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?s-u:.)&quot;</span>),
             <span class="ident">AnyByteNoNL</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?-u:.)&quot;</span>),
             <span class="ident">Class</span>(<span class="kw-2">ref</span> <span class="ident">cls</span>) <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}&quot;</span>, <span class="ident">cls</span>),
             <span class="ident">ClassBytes</span>(<span class="kw-2">ref</span> <span class="ident">cls</span>) <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}&quot;</span>, <span class="ident">cls</span>),
             <span class="ident">StartLine</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?m:^)&quot;</span>),
             <span class="ident">EndLine</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?m:$)&quot;</span>),
             <span class="ident">StartText</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">r&quot;^&quot;</span>),
             <span class="ident">EndText</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">r&quot;$&quot;</span>),
             <span class="ident">WordBoundary</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">r&quot;(?u:\b)&quot;</span>),
             <span class="ident">NotWordBoundary</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">r&quot;(?u:\B)&quot;</span>),
             <span class="ident">WordBoundaryAscii</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">r&quot;(?-u:\b)&quot;</span>),
             <span class="ident">NotWordBoundaryAscii</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">r&quot;(?-u:\B)&quot;</span>),
             <span class="ident">Group</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, <span class="ident">i</span>: <span class="prelude-val">None</span>, <span class="ident">name</span>: <span class="prelude-val">None</span> } <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?:{})&quot;</span>, <span class="ident">e</span>),
             <span class="ident">Group</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, <span class="ident">name</span>: <span class="prelude-val">None</span>, .. } <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;({})&quot;</span>, <span class="ident">e</span>),
             <span class="ident">Group</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, <span class="ident">name</span>: <span class="prelude-val">Some</span>(<span class="kw-2">ref</span> <span class="ident">n</span>), .. } <span class="op">=&gt;</span> {
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?P&lt;{}&gt;{})&quot;</span>, <span class="ident">n</span>, <span class="ident">e</span>)
             }
             <span class="ident">Repeat</span> { <span class="kw-2">ref</span> <span class="ident">e</span>, <span class="ident">r</span>, <span class="ident">greedy</span> } <span class="op">=&gt;</span> {
                 <span class="kw">match</span> <span class="kw-2">&amp;</span><span class="kw-2">*</span><span class="kw-2">*</span><span class="ident">e</span> {
                     <span class="kw-2">&amp;</span><span class="ident">Literal</span> { <span class="kw-2">ref</span> <span class="ident">chars</span>, .. } <span class="kw">if</span> <span class="ident">chars</span>.<span class="ident">len</span>() <span class="op">&gt;</span> <span class="number">1</span> <span class="op">=&gt;</span> {
                         <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?:{}){}&quot;</span>, <span class="ident">e</span>, <span class="ident">r</span>))
                     }
                     _ <span class="op">=&gt;</span> <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}{}&quot;</span>, <span class="ident">e</span>, <span class="ident">r</span>)),
                 }
                 <span class="kw">if</span> <span class="op">!</span><span class="ident">greedy</span> { <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;?&quot;</span>)); }
                 <span class="prelude-val">Ok</span>(())
             }
             <span class="ident">Concat</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> {
                 <span class="kw">for</span> <span class="ident">e</span> <span class="kw">in</span> <span class="ident">es</span> {
                     <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}&quot;</span>, <span class="ident">e</span>));
                 }
                 <span class="prelude-val">Ok</span>(())
             }
             <span class="ident">Alternate</span>(<span class="kw-2">ref</span> <span class="ident">es</span>) <span class="op">=&gt;</span> {
                 <span class="kw">for</span> (<span class="ident">i</span>, <span class="ident">e</span>) <span class="kw">in</span> <span class="ident">es</span>.<span class="ident">iter</span>().<span class="ident">enumerate</span>() {
                     <span class="kw">if</span> <span class="ident">i</span> <span class="op">&gt;</span> <span class="number">0</span> { <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;|&quot;</span>)); }
                     <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}&quot;</span>, <span class="ident">e</span>));
                 }
                 <span class="prelude-val">Ok</span>(())
             }
         }
     }
 }

 <span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">Repeater</span> {
     <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">ZeroOrOne</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;?&quot;</span>),
             <span class="ident">ZeroOrMore</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;*&quot;</span>),
             <span class="ident">OneOrMore</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;+&quot;</span>),
             <span class="ident">Range</span> { <span class="ident">min</span>: <span class="ident">s</span>, <span class="ident">max</span>: <span class="prelude-val">None</span> } <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{{{},}}&quot;</span>, <span class="ident">s</span>),
             <span class="ident">Range</span> { <span class="ident">min</span>: <span class="ident">s</span>, <span class="ident">max</span>: <span class="prelude-val">Some</span>(<span class="ident">e</span>) } <span class="kw">if</span> <span class="ident">s</span> <span class="op">==</span> <span class="ident">e</span> <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{{{}}}&quot;</span>, <span class="ident">s</span>),
             <span class="ident">Range</span> { <span class="ident">min</span>: <span class="ident">s</span>, <span class="ident">max</span>: <span class="prelude-val">Some</span>(<span class="ident">e</span>) } <span class="op">=&gt;</span> <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{{{}, {}}}&quot;</span>, <span class="ident">s</span>, <span class="ident">e</span>),
         }
     }
 }

 <span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">CharClass</span> {
     <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
         <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?u:[&quot;</span>));
         <span class="kw">for</span> <span class="ident">range</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">iter</span>() {
             <span class="kw">if</span> <span class="ident">range</span>.<span class="ident">start</span> <span class="op">==</span> <span class="string">&#39;-&#39;</span> <span class="op">||</span> <span class="ident">range</span>.<span class="ident">end</span> <span class="op">==</span> <span class="string">&#39;-&#39;</span> {
                 <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;-&quot;</span>));
                 <span class="kw">break</span>;
             }
         }
         <span class="kw">for</span> <span class="ident">range</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">iter</span>() {
             <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">range</span> <span class="op">=</span> <span class="kw-2">*</span><span class="ident">range</span>;
             <span class="kw">if</span> <span class="ident">range</span>.<span class="ident">start</span> <span class="op">==</span> <span class="string">&#39;-&#39;</span> {
                 <span class="ident">range</span>.<span class="ident">start</span> <span class="op">=</span> ((<span class="ident">range</span>.<span class="ident">start</span> <span class="kw">as</span> <span class="ident">u8</span>) <span class="op">+</span> <span class="number">1</span>) <span class="kw">as</span> <span class="ident">char</span>;
             }
             <span class="kw">if</span> <span class="ident">range</span>.<span class="ident">end</span> <span class="op">==</span> <span class="string">&#39;-&#39;</span> {
                 <span class="ident">range</span>.<span class="ident">end</span> <span class="op">=</span> ((<span class="ident">range</span>.<span class="ident">end</span> <span class="kw">as</span> <span class="ident">u8</span>) <span class="op">-</span> <span class="number">1</span>) <span class="kw">as</span> <span class="ident">char</span>;
             }
             <span class="kw">if</span> <span class="ident">range</span>.<span class="ident">start</span> <span class="op">&gt;</span> <span class="ident">range</span>.<span class="ident">end</span> {
                 <span class="kw">continue</span>;
             }
             <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}&quot;</span>, <span class="ident">range</span>));
         }
         <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;])&quot;</span>));
         <span class="prelude-val">Ok</span>(())
     }
 }

 <span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">ClassRange</span> {
     <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
         <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}-{}&quot;</span>, <span class="ident">quote_char</span>(<span class="self">self</span>.<span class="ident">start</span>), <span class="ident">quote_char</span>(<span class="self">self</span>.<span class="ident">end</span>))
     }
 }

 <span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">ByteClass</span> {
     <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
         <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;(?-u:[&quot;</span>));
         <span class="kw">for</span> <span class="ident">range</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">iter</span>() {
             <span class="kw">if</span> <span class="ident">range</span>.<span class="ident">start</span> <span class="op">==</span> <span class="string">b&#39;-&#39;</span> <span class="op">||</span> <span class="ident">range</span>.<span class="ident">end</span> <span class="op">==</span> <span class="string">b&#39;-&#39;</span> {
                 <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;-&quot;</span>));
                 <span class="kw">break</span>;
             }
         }
         <span class="kw">for</span> <span class="ident">range</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">iter</span>() {
             <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">range</span> <span class="op">=</span> <span class="kw-2">*</span><span class="ident">range</span>;
             <span class="kw">if</span> <span class="ident">range</span>.<span class="ident">start</span> <span class="op">==</span> <span class="string">b&#39;-&#39;</span> {
                 <span class="ident">range</span>.<span class="ident">start</span> <span class="op">+=</span> <span class="number">1</span>;
             }
             <span class="kw">if</span> <span class="ident">range</span>.<span class="ident">end</span> <span class="op">==</span> <span class="string">b&#39;-&#39;</span> {
                 <span class="ident">range</span>.<span class="ident">start</span> <span class="op">-=</span> <span class="number">1</span>;
             }
             <span class="kw">if</span> <span class="ident">range</span>.<span class="ident">start</span> <span class="op">&gt;</span> <span class="ident">range</span>.<span class="ident">end</span> {
                 <span class="kw">continue</span>;
             }
             <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}&quot;</span>, <span class="ident">range</span>));
         }
         <span class="macro">try</span><span class="macro">!</span>(<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;])&quot;</span>));
         <span class="prelude-val">Ok</span>(())
     }
 }

 <span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">ByteRange</span> {
     <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
         <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;{}-{}&quot;</span>, <span class="ident">quote_byte</span>(<span class="self">self</span>.<span class="ident">start</span>), <span class="ident">quote_byte</span>(<span class="self">self</span>.<span class="ident">end</span>))
     }
 }

 <span class="doccomment">/// An alias for computations that can return a `Error`.</span>
 <span class="kw">pub</span> <span class="kw">type</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> <span class="op">=</span> ::<span class="ident">std</span>::<span class="ident">result</span>::<span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">Error</span><span class="op">&gt;</span>;

 <span class="doccomment">/// A parse error.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// This includes details about the specific type of error and a rough</span>
 <span class="doccomment">/// approximation of where it occurred.</span>
 <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>)]</span>
 <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Error</span> {
     <span class="ident">pos</span>: <span class="ident">usize</span>,
     <span class="ident">surround</span>: <span class="ident">String</span>,
     <span class="ident">kind</span>: <span class="ident">ErrorKind</span>,
 }

 <span class="doccomment">/// The specific type of parse error that can occur.</span>
 <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>)]</span>
 <span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">ErrorKind</span> {
     <span class="doccomment">/// A negation symbol is used twice in flag settings.</span>
     <span class="doccomment">/// e.g., `(?-i-s)`.</span>
     <span class="ident">DoubleFlagNegation</span>,
     <span class="doccomment">/// The same capture name was used more than once.</span>
     <span class="doccomment">/// e.g., `(?P&lt;a&gt;.)(?P&lt;a&gt;.)`.</span>
     <span class="ident">DuplicateCaptureName</span>(<span class="ident">String</span>),
     <span class="doccomment">/// An alternate is empty. e.g., `(|a)`.</span>
     <span class="ident">EmptyAlternate</span>,
     <span class="doccomment">/// A capture group name is empty. e.g., `(?P&lt;&gt;a)`.</span>
     <span class="ident">EmptyCaptureName</span>,
     <span class="doccomment">/// A negation symbol was not proceded by any flags. e.g., `(?i-)`.</span>
     <span class="ident">EmptyFlagNegation</span>,
     <span class="doccomment">/// A group is empty. e.g., `()`.</span>
     <span class="ident">EmptyGroup</span>,
     <span class="doccomment">/// An invalid number was used in a counted repetition. e.g., `a{b}`.</span>
     <span class="ident">InvalidBase10</span>(<span class="ident">String</span>),
     <span class="doccomment">/// An invalid hexadecimal number was used in an escape sequence.</span>
     <span class="doccomment">/// e.g., `\xAG`.</span>
     <span class="ident">InvalidBase16</span>(<span class="ident">String</span>),
     <span class="doccomment">/// An invalid capture name was used. e.g., `(?P&lt;0a&gt;b)`.</span>
     <span class="ident">InvalidCaptureName</span>(<span class="ident">String</span>),
     <span class="doccomment">/// An invalid class range was givien. Specifically, when the start of the</span>
     <span class="doccomment">/// range is greater than the end. e.g., `[z-a]`.</span>
     <span class="ident">InvalidClassRange</span> {
         <span class="doccomment">/// The first character specified in the range.</span>
         <span class="ident">start</span>: <span class="ident">char</span>,
         <span class="doccomment">/// The second character specified in the range.</span>
         <span class="ident">end</span>: <span class="ident">char</span>,
     },
     <span class="doccomment">/// An escape sequence was used in a character class where it is not</span>
     <span class="doccomment">/// allowed. e.g., `[a-\pN]` or `[\A]`.</span>
     <span class="ident">InvalidClassEscape</span>(<span class="ident">Expr</span>),
     <span class="doccomment">/// An invalid counted repetition min/max was given. e.g., `a{2,1}`.</span>
     <span class="ident">InvalidRepeatRange</span> {
         <span class="doccomment">/// The first number specified in the repetition.</span>
         <span class="ident">min</span>: <span class="ident">u32</span>,
         <span class="doccomment">/// The second number specified in the repetition.</span>
         <span class="ident">max</span>: <span class="ident">u32</span>,
     },
     <span class="doccomment">/// An invalid Unicode scalar value was used in a long hexadecimal</span>
     <span class="doccomment">/// sequence. e.g., `\x{D800}`.</span>
     <span class="ident">InvalidScalarValue</span>(<span class="ident">u32</span>),
     <span class="doccomment">/// An empty counted repetition operator. e.g., `a{}`.</span>
     <span class="ident">MissingBase10</span>,
     <span class="doccomment">/// A repetition operator was not applied to an expression. e.g., `*`.</span>
     <span class="ident">RepeaterExpectsExpr</span>,
     <span class="doccomment">/// A repetition operator was applied to an expression that cannot be</span>
     <span class="doccomment">/// repeated. e.g., `a+*` or `a|*`.</span>
     <span class="ident">RepeaterUnexpectedExpr</span>(<span class="ident">Expr</span>),
     <span class="doccomment">/// A capture group name that is never closed. e.g., `(?P&lt;a`.</span>
     <span class="ident">UnclosedCaptureName</span>(<span class="ident">String</span>),
     <span class="doccomment">/// An unclosed hexadecimal literal. e.g., `\x{a`.</span>
     <span class="ident">UnclosedHex</span>,
     <span class="doccomment">/// An unclosed parenthesis. e.g., `(a`.</span>
     <span class="ident">UnclosedParen</span>,
     <span class="doccomment">/// An unclosed counted repetition operator. e.g., `a{2`.</span>
     <span class="ident">UnclosedRepeat</span>,
     <span class="doccomment">/// An unclosed named Unicode class. e.g., `\p{Yi`.</span>
     <span class="ident">UnclosedUnicodeName</span>,
     <span class="doccomment">/// Saw end of regex before class was closed. e.g., `[a`.</span>
     <span class="ident">UnexpectedClassEof</span>,
     <span class="doccomment">/// Saw end of regex before escape sequence was closed. e.g., `\`.</span>
     <span class="ident">UnexpectedEscapeEof</span>,
     <span class="doccomment">/// Saw end of regex before flags were closed. e.g., `(?i`.</span>
     <span class="ident">UnexpectedFlagEof</span>,
     <span class="doccomment">/// Saw end of regex before two hexadecimal digits were seen. e.g., `\xA`.</span>
     <span class="ident">UnexpectedTwoDigitHexEof</span>,
     <span class="doccomment">/// Unopened parenthesis. e.g., `)`.</span>
     <span class="ident">UnopenedParen</span>,
     <span class="doccomment">/// Unrecognized escape sequence. e.g., `\q`.</span>
     <span class="ident">UnrecognizedEscape</span>(<span class="ident">char</span>),
     <span class="doccomment">/// Unrecognized flag. e.g., `(?a)`.</span>
     <span class="ident">UnrecognizedFlag</span>(<span class="ident">char</span>),
     <span class="doccomment">/// Unrecognized named Unicode class. e.g., `\p{Foo}`.</span>
     <span class="ident">UnrecognizedUnicodeClass</span>(<span class="ident">String</span>),
     <span class="doccomment">/// Indicates that the regex uses too much nesting.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// (N.B. This error exists because traversing the Expr is recursive and</span>
     <span class="doccomment">/// an explicit heap allocated stack is not (yet?) used. Regardless, some</span>
     <span class="doccomment">/// sort of limit must be applied to avoid unbounded memory growth.</span>
     <span class="ident">StackExhausted</span>,
     <span class="doccomment">/// A disallowed flag was found (e.g., `u`).</span>
     <span class="ident">FlagNotAllowed</span>(<span class="ident">char</span>),
     <span class="doccomment">/// A Unicode class was used when the Unicode (`u`) flag was disabled.</span>
     <span class="ident">UnicodeNotAllowed</span>,
     <span class="doccomment">/// InvalidUtf8 indicates that the expression may match non-UTF-8 bytes.</span>
     <span class="doccomment">/// This never returned if the parser is permitted to allow expressions</span>
     <span class="doccomment">/// that match arbitrary bytes.</span>
     <span class="ident">InvalidUtf8</span>,
     <span class="doccomment">/// A character class was constructed such that it is empty.</span>
     <span class="doccomment">/// e.g., `[^\d\D]`.</span>
     <span class="ident">EmptyClass</span>,
     <span class="doccomment">/// Hints that destructuring should not be exhaustive.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// This enum may grow additional variants, so this makes sure clients</span>
     <span class="doccomment">/// don&#39;t count on exhaustive matching. (Otherwise, adding a new variant</span>
     <span class="doccomment">/// could break existing code.)</span>
     <span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
     <span class="ident">__Nonexhaustive</span>,
 }

 <span class="kw">impl</span> <span class="ident">Error</span> {
     <span class="doccomment">/// Returns an approximate *character* offset at which the error occurred.</span>
     <span class="doccomment">///</span>
     <span class="doccomment">/// The character offset may be equal to the number of characters in the</span>
     <span class="doccomment">/// string, in which case it should be interpreted as pointing to the end</span>
     <span class="doccomment">/// of the regex.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">position</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
         <span class="self">self</span>.<span class="ident">pos</span>
     }

     <span class="doccomment">/// Returns the type of the regex parse error.</span>
     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">kind</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">ErrorKind</span> {
         <span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">kind</span>
     }
 }

 <span class="kw">impl</span> <span class="ident">ErrorKind</span> {
     <span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">str</span> {
         <span class="kw">use</span> <span class="ident">ErrorKind</span>::<span class="kw-2">*</span>;
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">DoubleFlagNegation</span> <span class="op">=&gt;</span> <span class="string">&quot;double flag negation&quot;</span>,
             <span class="ident">DuplicateCaptureName</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;duplicate capture name&quot;</span>,
             <span class="ident">EmptyAlternate</span> <span class="op">=&gt;</span> <span class="string">&quot;empty alternate&quot;</span>,
             <span class="ident">EmptyCaptureName</span> <span class="op">=&gt;</span> <span class="string">&quot;empty capture name&quot;</span>,
             <span class="ident">EmptyFlagNegation</span> <span class="op">=&gt;</span> <span class="string">&quot;flag negation without any flags&quot;</span>,
             <span class="ident">EmptyGroup</span> <span class="op">=&gt;</span> <span class="string">&quot;empty group (e.g., &#39;()&#39;)&quot;</span>,
             <span class="ident">InvalidBase10</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;invalid base 10 number&quot;</span>,
             <span class="ident">InvalidBase16</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;invalid base 16 number&quot;</span>,
             <span class="ident">InvalidCaptureName</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;invalid capture name&quot;</span>,
             <span class="ident">InvalidClassRange</span>{..} <span class="op">=&gt;</span> <span class="string">&quot;invalid character class range&quot;</span>,
             <span class="ident">InvalidClassEscape</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;invalid escape sequence in class&quot;</span>,
             <span class="ident">InvalidRepeatRange</span>{..} <span class="op">=&gt;</span> <span class="string">&quot;invalid counted repetition range&quot;</span>,
             <span class="ident">InvalidScalarValue</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;invalid Unicode scalar value&quot;</span>,
             <span class="ident">MissingBase10</span> <span class="op">=&gt;</span> <span class="string">&quot;missing count in repetition operator&quot;</span>,
             <span class="ident">RepeaterExpectsExpr</span> <span class="op">=&gt;</span> <span class="string">&quot;repetition operator missing expression&quot;</span>,
             <span class="ident">RepeaterUnexpectedExpr</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;expression cannot be repeated&quot;</span>,
             <span class="ident">UnclosedCaptureName</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;unclosed capture group name&quot;</span>,
             <span class="ident">UnclosedHex</span> <span class="op">=&gt;</span> <span class="string">&quot;unclosed hexadecimal literal&quot;</span>,
             <span class="ident">UnclosedParen</span> <span class="op">=&gt;</span> <span class="string">&quot;unclosed parenthesis&quot;</span>,
             <span class="ident">UnclosedRepeat</span> <span class="op">=&gt;</span> <span class="string">&quot;unclosed counted repetition operator&quot;</span>,
             <span class="ident">UnclosedUnicodeName</span> <span class="op">=&gt;</span> <span class="string">&quot;unclosed Unicode class literal&quot;</span>,
             <span class="ident">UnexpectedClassEof</span> <span class="op">=&gt;</span> <span class="string">&quot;unexpected EOF in character class&quot;</span>,
             <span class="ident">UnexpectedEscapeEof</span> <span class="op">=&gt;</span> <span class="string">&quot;unexpected EOF in escape sequence&quot;</span>,
             <span class="ident">UnexpectedFlagEof</span> <span class="op">=&gt;</span> <span class="string">&quot;unexpected EOF in flags&quot;</span>,
             <span class="ident">UnexpectedTwoDigitHexEof</span> <span class="op">=&gt;</span> <span class="string">&quot;unexpected EOF in hex literal&quot;</span>,
             <span class="ident">UnopenedParen</span> <span class="op">=&gt;</span> <span class="string">&quot;unopened parenthesis&quot;</span>,
             <span class="ident">UnrecognizedEscape</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;unrecognized escape sequence&quot;</span>,
             <span class="ident">UnrecognizedFlag</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;unrecognized flag&quot;</span>,
             <span class="ident">UnrecognizedUnicodeClass</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;unrecognized Unicode class name&quot;</span>,
             <span class="ident">StackExhausted</span> <span class="op">=&gt;</span> <span class="string">&quot;stack exhausted, too much nesting&quot;</span>,
             <span class="ident">FlagNotAllowed</span>(_) <span class="op">=&gt;</span> <span class="string">&quot;flag not allowed&quot;</span>,
             <span class="ident">UnicodeNotAllowed</span> <span class="op">=&gt;</span> <span class="string">&quot;Unicode features not allowed&quot;</span>,
             <span class="ident">InvalidUtf8</span> <span class="op">=&gt;</span> <span class="string">&quot;matching arbitrary bytes is not allowed&quot;</span>,
             <span class="ident">EmptyClass</span> <span class="op">=&gt;</span> <span class="string">&quot;empty character class&quot;</span>,
             <span class="ident">__Nonexhaustive</span> <span class="op">=&gt;</span> <span class="macro">unreachable</span><span class="macro">!</span>(),
         }
     }
 }

 <span class="kw">impl</span> ::<span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span> <span class="kw">for</span> <span class="ident">Error</span> {
     <span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">str</span> {
         <span class="self">self</span>.<span class="ident">kind</span>.<span class="ident">description</span>()
     }
 }

 <span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">Error</span> {
     <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
         <span class="kw">if</span> <span class="kw">let</span> <span class="ident">ErrorKind</span>::<span class="ident">StackExhausted</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">kind</span> {
             <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Error parsing regex: {}&quot;</span>, <span class="self">self</span>.<span class="ident">kind</span>)
         } <span class="kw">else</span> {
             <span class="macro">write</span><span class="macro">!</span>(
                 <span class="ident">f</span>, <span class="string">&quot;Error parsing regex near &#39;{}&#39; at character offset {}: {}&quot;</span>,
                 <span class="self">self</span>.<span class="ident">surround</span>, <span class="self">self</span>.<span class="ident">pos</span>, <span class="self">self</span>.<span class="ident">kind</span>)
         }
     }
 }

 <span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">ErrorKind</span> {
     <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
         <span class="kw">use</span> <span class="ident">ErrorKind</span>::<span class="kw-2">*</span>;
         <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
             <span class="ident">DoubleFlagNegation</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Only one negation symbol is allowed in flags.&quot;</span>),
             <span class="ident">DuplicateCaptureName</span>(<span class="kw-2">ref</span> <span class="ident">s</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Capture name &#39;{}&#39; is used more than once.&quot;</span>, <span class="ident">s</span>),
             <span class="ident">EmptyAlternate</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Alternations cannot be empty.&quot;</span>),
             <span class="ident">EmptyCaptureName</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Capture names cannot be empty.&quot;</span>),
             <span class="ident">EmptyFlagNegation</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Flag negation requires setting at least one flag.&quot;</span>),
             <span class="ident">EmptyGroup</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Empty regex groups (e.g., &#39;()&#39;) are not allowed.&quot;</span>),
             <span class="ident">InvalidBase10</span>(<span class="kw-2">ref</span> <span class="ident">s</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Not a valid base 10 number: &#39;{}&#39;&quot;</span>, <span class="ident">s</span>),
             <span class="ident">InvalidBase16</span>(<span class="kw-2">ref</span> <span class="ident">s</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Not a valid base 16 number: &#39;{}&#39;&quot;</span>, <span class="ident">s</span>),
             <span class="ident">InvalidCaptureName</span>(<span class="kw-2">ref</span> <span class="ident">s</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Invalid capture name: &#39;{}&#39;. Capture names must \
                            consist of [_a-zA-Z0-9] and are not allowed to \
                            start with with a number.&quot;</span>, <span class="ident">s</span>),
             <span class="ident">InvalidClassRange</span> { <span class="ident">start</span>, <span class="ident">end</span> } <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Invalid character class range &#39;{}-{}&#39;. \
                            Character class ranges must start with the smaller \
                            character, but {} &gt; {}&quot;</span>, <span class="ident">start</span>, <span class="ident">end</span>, <span class="ident">start</span>, <span class="ident">end</span>),
             <span class="ident">InvalidClassEscape</span>(<span class="kw-2">ref</span> <span class="ident">e</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Invalid escape sequence in character \
                            class: &#39;{}&#39;.&quot;</span>, <span class="ident">e</span>),
             <span class="ident">InvalidRepeatRange</span> { <span class="ident">min</span>, <span class="ident">max</span> } <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Invalid counted repetition range: {{{}, {}}}. \
                            Counted repetition ranges must start with the \
                            minimum, but {} &gt; {}&quot;</span>, <span class="ident">min</span>, <span class="ident">max</span>, <span class="ident">min</span>, <span class="ident">max</span>),
             <span class="ident">InvalidScalarValue</span>(<span class="ident">c</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Number does not correspond to a Unicode scalar \
                            value: &#39;{}&#39;.&quot;</span>, <span class="ident">c</span>),
             <span class="ident">MissingBase10</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Missing maximum in counted reptition operator.&quot;</span>),
             <span class="ident">RepeaterExpectsExpr</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Missing expression for reptition operator.&quot;</span>),
             <span class="ident">RepeaterUnexpectedExpr</span>(<span class="kw-2">ref</span> <span class="ident">e</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Invalid application of reptition operator to: \
                           &#39;{}&#39;.&quot;</span>, <span class="ident">e</span>),
             <span class="ident">UnclosedCaptureName</span>(<span class="kw-2">ref</span> <span class="ident">s</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Capture name group for &#39;{}&#39; is not closed. \
                            (Missing a &#39;&gt;&#39;.)&quot;</span>, <span class="ident">s</span>),
             <span class="ident">UnclosedHex</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unclosed hexadecimal literal (missing a &#39;}}&#39;).&quot;</span>),
             <span class="ident">UnclosedParen</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unclosed parenthesis.&quot;</span>),
             <span class="ident">UnclosedRepeat</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unclosed counted repetition (missing a &#39;}}&#39;).&quot;</span>),
             <span class="ident">UnclosedUnicodeName</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unclosed Unicode literal (missing a &#39;}}&#39;).&quot;</span>),
             <span class="ident">UnexpectedClassEof</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Character class was not closed before the end of \
                            the regex (missing a &#39;]&#39;).&quot;</span>),
             <span class="ident">UnexpectedEscapeEof</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Started an escape sequence that didn&#39;t finish \
                            before the end of the regex.&quot;</span>),
             <span class="ident">UnexpectedFlagEof</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Inline flag settings was not closed before the end \
                            of the regex (missing a &#39;)&#39; or &#39;:&#39;).&quot;</span>),
             <span class="ident">UnexpectedTwoDigitHexEof</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unexpected end of two digit hexadecimal literal.&quot;</span>),
             <span class="ident">UnopenedParen</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unopened parenthesis.&quot;</span>),
             <span class="ident">UnrecognizedEscape</span>(<span class="ident">c</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unrecognized escape sequence: &#39;\\{}&#39;.&quot;</span>, <span class="ident">c</span>),
             <span class="ident">UnrecognizedFlag</span>(<span class="ident">c</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unrecognized flag: &#39;{}&#39;. \
                            (Allowed flags: i, m, s, U, u, x.)&quot;</span>, <span class="ident">c</span>),
             <span class="ident">UnrecognizedUnicodeClass</span>(<span class="kw-2">ref</span> <span class="ident">s</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unrecognized Unicode class name: &#39;{}&#39;.&quot;</span>, <span class="ident">s</span>),
             <span class="ident">StackExhausted</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Exhausted space required to parse regex with too \
                            much nesting.&quot;</span>),
             <span class="ident">FlagNotAllowed</span>(<span class="ident">flag</span>) <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Use of the flag &#39;{}&#39; is not allowed.&quot;</span>, <span class="ident">flag</span>),
             <span class="ident">UnicodeNotAllowed</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Unicode features are not allowed when the Unicode \
                            (u) flag is not set.&quot;</span>),
             <span class="ident">InvalidUtf8</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Matching arbitrary bytes is not allowed.&quot;</span>),
             <span class="ident">EmptyClass</span> <span class="op">=&gt;</span>
                 <span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">&quot;Empty character classes are not allowed.&quot;</span>),
             <span class="ident">__Nonexhaustive</span> <span class="op">=&gt;</span> <span class="macro">unreachable</span><span class="macro">!</span>(),
         }
     }
 }

 <span class="doccomment">/// The result of binary search on the simple case folding table.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// Note that this binary search is done on the &quot;both&quot; table, such that</span>
 <span class="doccomment">/// the index returned corresponds to the *first* location of `c1` in the</span>
 <span class="doccomment">/// table. The table can then be scanned linearly starting from the position</span>
 <span class="doccomment">/// returned to find other case mappings for `c1`.</span>
 <span class="kw">fn</span> <span class="ident">simple_case_fold_both_result</span>(<span class="ident">c1</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">result</span>::<span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">usize</span>, <span class="ident">usize</span><span class="op">&gt;</span> {
     <span class="kw">let</span> <span class="ident">table</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="ident">case_folding</span>::<span class="ident">C_plus_S_both_table</span>;
     <span class="kw">let</span> <span class="ident">i</span> <span class="op">=</span> <span class="ident">binary_search</span>(<span class="ident">table</span>, <span class="op">|</span><span class="kw-2">&amp;</span>(<span class="ident">c2</span>, _)<span class="op">|</span> <span class="ident">c1</span> <span class="op">&lt;=</span> <span class="ident">c2</span>);
     <span class="kw">if</span> <span class="ident">i</span> <span class="op">&gt;=</span> <span class="ident">table</span>.<span class="ident">len</span>() <span class="op">||</span> <span class="ident">table</span>[<span class="ident">i</span>].<span class="number">0</span> <span class="op">!=</span> <span class="ident">c1</span> {
         <span class="prelude-val">Err</span>(<span class="ident">i</span>)
     } <span class="kw">else</span> {
         <span class="prelude-val">Ok</span>(<span class="ident">i</span>)
     }
 }

 <span class="doccomment">/// Binary search to find first element such that `pred(T) == true`.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// Assumes that if `pred(xs[i]) == true` then `pred(xs[i+1]) == true`.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// If all elements yield `pred(T) == false`, then `xs.len()` is returned.</span>
 <span class="kw">fn</span> <span class="ident">binary_search</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">F</span><span class="op">&gt;</span>(<span class="ident">xs</span>: <span class="kw-2">&amp;</span>[<span class="ident">T</span>], <span class="kw-2">mut</span> <span class="ident">pred</span>: <span class="ident">F</span>) <span class="op">-&gt;</span> <span class="ident">usize</span>
         <span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnMut</span>(<span class="kw-2">&amp;</span><span class="ident">T</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
     <span class="kw">let</span> (<span class="kw-2">mut</span> <span class="ident">left</span>, <span class="kw-2">mut</span> <span class="ident">right</span>) <span class="op">=</span> (<span class="number">0</span>, <span class="ident">xs</span>.<span class="ident">len</span>());
     <span class="kw">while</span> <span class="ident">left</span> <span class="op">&lt;</span> <span class="ident">right</span> {
         <span class="kw">let</span> <span class="ident">mid</span> <span class="op">=</span> (<span class="ident">left</span> <span class="op">+</span> <span class="ident">right</span>) <span class="op">/</span> <span class="number">2</span>;
         <span class="kw">if</span> <span class="ident">pred</span>(<span class="kw-2">&amp;</span><span class="ident">xs</span>[<span class="ident">mid</span>]) {
             <span class="ident">right</span> <span class="op">=</span> <span class="ident">mid</span>;
         } <span class="kw">else</span> {
             <span class="ident">left</span> <span class="op">=</span> <span class="ident">mid</span> <span class="op">+</span> <span class="number">1</span>;
         }
     }
     <span class="ident">left</span>
 }

 <span class="doccomment">/// Escapes all regular expression meta characters in `text`.</span>
 <span class="doccomment">///</span>
 <span class="doccomment">/// The string returned may be safely used as a literal in a regular</span>
 <span class="doccomment">/// expression.</span>
 <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">quote</span>(<span class="ident">text</span>: <span class="kw-2">&amp;</span><span class="ident">str</span>) <span class="op">-&gt;</span> <span class="ident">String</span> {
     <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">quoted</span> <span class="op">=</span> <span class="ident">String</span>::<span class="ident">with_capacity</span>(<span class="ident">text</span>.<span class="ident">len</span>());
     <span class="kw">for</span> <span class="ident">c</span> <span class="kw">in</span> <span class="ident">text</span>.<span class="ident">chars</span>() {
         <span class="kw">if</span> <span class="ident">parser</span>::<span class="ident">is_punct</span>(<span class="ident">c</span>) {
             <span class="ident">quoted</span>.<span class="ident">push</span>(<span class="string">&#39;\\&#39;</span>);
         }
         <span class="ident">quoted</span>.<span class="ident">push</span>(<span class="ident">c</span>);
     }
     <span class="ident">quoted</span>
 }

 <span class="kw">fn</span> <span class="ident">quote_char</span>(<span class="ident">c</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">String</span> {
     <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">s</span> <span class="op">=</span> <span class="ident">String</span>::<span class="ident">new</span>();
     <span class="kw">if</span> <span class="ident">parser</span>::<span class="ident">is_punct</span>(<span class="ident">c</span>) {
         <span class="ident">s</span>.<span class="ident">push</span>(<span class="string">&#39;\\&#39;</span>);
     }
     <span class="ident">s</span>.<span class="ident">push</span>(<span class="ident">c</span>);
     <span class="ident">s</span>
 }

 <span class="kw">fn</span> <span class="ident">quote_byte</span>(<span class="ident">b</span>: <span class="ident">u8</span>) <span class="op">-&gt;</span> <span class="ident">String</span> {
     <span class="kw">if</span> <span class="ident">parser</span>::<span class="ident">is_punct</span>(<span class="ident">b</span> <span class="kw">as</span> <span class="ident">char</span>) <span class="op">||</span> <span class="ident">b</span> <span class="op">==</span> <span class="string">b&#39;\&#39;&#39;</span> <span class="op">||</span> <span class="ident">b</span> <span class="op">==</span> <span class="string">b&#39;&quot;&#39;</span> {
         <span class="ident">quote_char</span>(<span class="ident">b</span> <span class="kw">as</span> <span class="ident">char</span>)
     } <span class="kw">else</span> {
         <span class="kw">let</span> <span class="ident">escaped</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">u8</span><span class="op">&gt;</span> <span class="op">=</span> <span class="ident">ascii</span>::<span class="ident">escape_default</span>(<span class="ident">b</span>).<span class="ident">collect</span>();
         <span class="ident">String</span>::<span class="ident">from_utf8</span>(<span class="ident">escaped</span>).<span class="ident">unwrap</span>()
     }
 }

 <span class="kw">fn</span> <span class="ident">inc_char</span>(<span class="ident">c</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">char</span> {
     <span class="kw">match</span> <span class="ident">c</span> {
         <span class="ident">char</span>::<span class="ident">MAX</span> <span class="op">=&gt;</span> <span class="ident">char</span>::<span class="ident">MAX</span>,
         <span class="string">&#39;\u{D7FF}&#39;</span> <span class="op">=&gt;</span> <span class="string">&#39;\u{E000}&#39;</span>,
         <span class="ident">c</span> <span class="op">=&gt;</span> <span class="ident">char</span>::<span class="ident">from_u32</span>(<span class="ident">c</span> <span class="kw">as</span> <span class="ident">u32</span> <span class="op">+</span> <span class="number">1</span>).<span class="ident">unwrap</span>(),
     }
 }

 <span class="kw">fn</span> <span class="ident">dec_char</span>(<span class="ident">c</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">char</span> {
     <span class="kw">match</span> <span class="ident">c</span> {
         <span class="string">&#39;\x00&#39;</span> <span class="op">=&gt;</span> <span class="string">&#39;\x00&#39;</span>,
         <span class="string">&#39;\u{E000}&#39;</span> <span class="op">=&gt;</span> <span class="string">&#39;\u{D7FF}&#39;</span>,
         <span class="ident">c</span> <span class="op">=&gt;</span> <span class="ident">char</span>::<span class="ident">from_u32</span>(<span class="ident">c</span> <span class="kw">as</span> <span class="ident">u32</span> <span class="op">-</span> <span class="number">1</span>).<span class="ident">unwrap</span>(),
     }
 }

 <span class="doccomment">/// Returns true if and only if `c` is a word character.</span>
 <span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
 <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is_word_char</span>(<span class="ident">c</span>: <span class="ident">char</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
     <span class="kw">match</span> <span class="ident">c</span> {
         <span class="string">&#39;_&#39;</span> <span class="op">|</span> <span class="string">&#39;0&#39;</span> ... <span class="string">&#39;9&#39;</span> <span class="op">|</span> <span class="string">&#39;a&#39;</span> ... <span class="string">&#39;z&#39;</span> <span class="op">|</span> <span class="string">&#39;A&#39;</span> ... <span class="string">&#39;Z&#39;</span>  <span class="op">=&gt;</span> <span class="bool-val">true</span>,
         _ <span class="op">=&gt;</span> ::<span class="ident">unicode</span>::<span class="ident">regex</span>::<span class="ident">PERLW</span>.<span class="ident">binary_search_by</span>(<span class="op">|</span><span class="kw-2">&amp;</span>(<span class="ident">start</span>, <span class="ident">end</span>)<span class="op">|</span> {
             <span class="kw">if</span> <span class="ident">c</span> <span class="op">&gt;=</span> <span class="ident">start</span> <span class="op">&amp;&amp;</span> <span class="ident">c</span> <span class="op">&lt;=</span> <span class="ident">end</span> {
                 <span class="ident">Ordering</span>::<span class="ident">Equal</span>
             } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">start</span> <span class="op">&gt;</span> <span class="ident">c</span> {
                 <span class="ident">Ordering</span>::<span class="ident">Greater</span>
             } <span class="kw">else</span> {
                 <span class="ident">Ordering</span>::<span class="ident">Less</span>
             }
         }).<span class="ident">is_ok</span>(),
     }
 }

 <span class="doccomment">/// Returns true if and only if `c` is an ASCII word byte.</span>
 <span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
 <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is_word_byte</span>(<span class="ident">b</span>: <span class="ident">u8</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
     <span class="kw">match</span> <span class="ident">b</span> {
         <span class="string">b&#39;_&#39;</span> <span class="op">|</span> <span class="string">b&#39;0&#39;</span> ... <span class="string">b&#39;9&#39;</span> <span class="op">|</span> <span class="string">b&#39;a&#39;</span> ... <span class="string">b&#39;z&#39;</span> <span class="op">|</span> <span class="string">b&#39;A&#39;</span> ... <span class="string">b&#39;Z&#39;</span>  <span class="op">=&gt;</span> <span class="bool-val">true</span>,
         _ <span class="op">=&gt;</span> <span class="bool-val">false</span>,
     }
 }

 <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
 <span class="kw">mod</span> <span class="ident">properties</span>;

 <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
 <span class="kw">mod</span> <span class="ident">tests</span> {
     <span class="kw">use</span> {<span class="ident">CharClass</span>, <span class="ident">ClassRange</span>, <span class="ident">ByteClass</span>, <span class="ident">ByteRange</span>, <span class="ident">Expr</span>};

     <span class="kw">fn</span> <span class="ident">class</span>(<span class="ident">ranges</span>: <span class="kw-2">&amp;</span>[(<span class="ident">char</span>, <span class="ident">char</span>)]) <span class="op">-&gt;</span> <span class="ident">CharClass</span> {
         <span class="kw">let</span> <span class="ident">ranges</span> <span class="op">=</span> <span class="ident">ranges</span>.<span class="ident">iter</span>().<span class="ident">cloned</span>()
                            .<span class="ident">map</span>(<span class="op">|</span>(<span class="ident">c1</span>, <span class="ident">c2</span>)<span class="op">|</span> <span class="ident">ClassRange</span>::<span class="ident">new</span>(<span class="ident">c1</span>, <span class="ident">c2</span>)).<span class="ident">collect</span>();
         <span class="ident">CharClass</span>::<span class="ident">new</span>(<span class="ident">ranges</span>)
     }

     <span class="kw">fn</span> <span class="ident">bclass</span>(<span class="ident">ranges</span>: <span class="kw-2">&amp;</span>[(<span class="ident">u8</span>, <span class="ident">u8</span>)]) <span class="op">-&gt;</span> <span class="ident">ByteClass</span> {
         <span class="kw">let</span> <span class="ident">ranges</span> <span class="op">=</span> <span class="ident">ranges</span>.<span class="ident">iter</span>().<span class="ident">cloned</span>()
                            .<span class="ident">map</span>(<span class="op">|</span>(<span class="ident">c1</span>, <span class="ident">c2</span>)<span class="op">|</span> <span class="ident">ByteRange</span>::<span class="ident">new</span>(<span class="ident">c1</span>, <span class="ident">c2</span>)).<span class="ident">collect</span>();
         <span class="ident">ByteClass</span>::<span class="ident">new</span>(<span class="ident">ranges</span>)
     }

     <span class="kw">fn</span> <span class="ident">e</span>(<span class="ident">re</span>: <span class="kw-2">&amp;</span><span class="ident">str</span>) <span class="op">-&gt;</span> <span class="ident">Expr</span> { <span class="ident">Expr</span>::<span class="ident">parse</span>(<span class="ident">re</span>).<span class="ident">unwrap</span>() }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">stack_exhaustion</span>() {
         <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">iter</span>::<span class="ident">repeat</span>;

         <span class="kw">let</span> <span class="ident">open</span>: <span class="ident">String</span> <span class="op">=</span> <span class="ident">repeat</span>(<span class="string">&#39;(&#39;</span>).<span class="ident">take</span>(<span class="number">200</span>).<span class="ident">collect</span>();
         <span class="kw">let</span> <span class="ident">close</span>: <span class="ident">String</span> <span class="op">=</span> <span class="ident">repeat</span>(<span class="string">&#39;)&#39;</span>).<span class="ident">take</span>(<span class="number">200</span>).<span class="ident">collect</span>();
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">Expr</span>::<span class="ident">parse</span>(<span class="kw-2">&amp;</span><span class="macro">format</span><span class="macro">!</span>(<span class="string">&quot;{}a{}&quot;</span>, <span class="ident">open</span>, <span class="ident">close</span>)).<span class="ident">is_ok</span>());

         <span class="kw">let</span> <span class="ident">open</span>: <span class="ident">String</span> <span class="op">=</span> <span class="ident">repeat</span>(<span class="string">&#39;(&#39;</span>).<span class="ident">take</span>(<span class="number">200</span> <span class="op">+</span> <span class="number">1</span>).<span class="ident">collect</span>();
         <span class="kw">let</span> <span class="ident">close</span>: <span class="ident">String</span> <span class="op">=</span> <span class="ident">repeat</span>(<span class="string">&#39;)&#39;</span>).<span class="ident">take</span>(<span class="number">200</span> <span class="op">+</span> <span class="number">1</span>).<span class="ident">collect</span>();
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">Expr</span>::<span class="ident">parse</span>(<span class="kw-2">&amp;</span><span class="macro">format</span><span class="macro">!</span>(<span class="string">&quot;{}a{}&quot;</span>, <span class="ident">open</span>, <span class="ident">close</span>)).<span class="ident">is_err</span>());
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">anchored_start</span>() {
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;^a&quot;</span>).<span class="ident">is_anchored_start</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;(^a)&quot;</span>).<span class="ident">is_anchored_start</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;^a|^b&quot;</span>).<span class="ident">is_anchored_start</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;(^a)|(^b)&quot;</span>).<span class="ident">is_anchored_start</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;(^(a|b))&quot;</span>).<span class="ident">is_anchored_start</span>());

         <span class="macro">assert</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">e</span>(<span class="string">&quot;^a|b&quot;</span>).<span class="ident">is_anchored_start</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">e</span>(<span class="string">&quot;a|^b&quot;</span>).<span class="ident">is_anchored_start</span>());
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">anchored_end</span>() {
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;a$&quot;</span>).<span class="ident">is_anchored_end</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;(a$)&quot;</span>).<span class="ident">is_anchored_end</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;a$|b$&quot;</span>).<span class="ident">is_anchored_end</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;(a$)|(b$)&quot;</span>).<span class="ident">is_anchored_end</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">e</span>(<span class="string">&quot;((a|b)$)&quot;</span>).<span class="ident">is_anchored_end</span>());

         <span class="macro">assert</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">e</span>(<span class="string">&quot;a$|b&quot;</span>).<span class="ident">is_anchored_end</span>());
         <span class="macro">assert</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">e</span>(<span class="string">&quot;a|b$&quot;</span>).<span class="ident">is_anchored_end</span>());
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_canon_no_change</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;a&#39;</span>, <span class="string">&#39;c&#39;</span>), (<span class="string">&#39;x&#39;</span>, <span class="string">&#39;z&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">canonicalize</span>(), <span class="ident">cls</span>);
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_canon_unordered</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;x&#39;</span>, <span class="string">&#39;z&#39;</span>), (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;c&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">canonicalize</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;c&#39;</span>), (<span class="string">&#39;x&#39;</span>, <span class="string">&#39;z&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_canon_overlap</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;x&#39;</span>, <span class="string">&#39;z&#39;</span>), (<span class="string">&#39;w&#39;</span>, <span class="string">&#39;y&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">canonicalize</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;w&#39;</span>, <span class="string">&#39;z&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_canon_overlap_many</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;c&#39;</span>, <span class="string">&#39;f&#39;</span>), (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;g&#39;</span>), (<span class="string">&#39;d&#39;</span>, <span class="string">&#39;j&#39;</span>), (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;c&#39;</span>),
             (<span class="string">&#39;m&#39;</span>, <span class="string">&#39;p&#39;</span>), (<span class="string">&#39;l&#39;</span>, <span class="string">&#39;s&#39;</span>),
         ]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">canonicalize</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;j&#39;</span>), (<span class="string">&#39;l&#39;</span>, <span class="string">&#39;s&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_canon_overlap_boundary</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;x&#39;</span>, <span class="string">&#39;z&#39;</span>), (<span class="string">&#39;u&#39;</span>, <span class="string">&#39;w&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">canonicalize</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;u&#39;</span>, <span class="string">&#39;z&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_canon_extreme_edge_case</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>), (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">canonicalize</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_canon_singles</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;a&#39;</span>, <span class="string">&#39;a&#39;</span>), (<span class="string">&#39;b&#39;</span>, <span class="string">&#39;b&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">canonicalize</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;a&#39;</span>, <span class="string">&#39;b&#39;</span>)]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_single</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;a&#39;</span>, <span class="string">&#39;a&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\x60&#39;</span>), (<span class="string">&#39;\x62&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_singles</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;a&#39;</span>, <span class="string">&#39;a&#39;</span>), (<span class="string">&#39;b&#39;</span>, <span class="string">&#39;b&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\x60&#39;</span>), (<span class="string">&#39;\x63&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_multiples</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;a&#39;</span>, <span class="string">&#39;c&#39;</span>), (<span class="string">&#39;x&#39;</span>, <span class="string">&#39;z&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\x60&#39;</span>), (<span class="string">&#39;\x64&#39;</span>, <span class="string">&#39;\x77&#39;</span>), (<span class="string">&#39;\x7b&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_min_scalar</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;a&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x62&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_max_scalar</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;a&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\x60&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_everything</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_everything_sans_one</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\u{10FFFD}&#39;</span>), (<span class="string">&#39;\u{10FFFF}&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>)
         ]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\u{10FFFE}&#39;</span>, <span class="string">&#39;\u{10FFFE}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_surrogates_min</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\u{D7FF}&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\u{E000}&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_surrogates_min_edge</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\u{D7FE}&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\u{D7FF}&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_surrogates_max</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;\u{E000}&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\u{D7FF}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_negate_surrogates_max_edge</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;\u{E001}&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\u{E000}&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_canon_overlap_many_case_fold</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;C&#39;</span>, <span class="string">&#39;F&#39;</span>), (<span class="string">&#39;A&#39;</span>, <span class="string">&#39;G&#39;</span>), (<span class="string">&#39;D&#39;</span>, <span class="string">&#39;J&#39;</span>), (<span class="string">&#39;A&#39;</span>, <span class="string">&#39;C&#39;</span>),
             (<span class="string">&#39;M&#39;</span>, <span class="string">&#39;P&#39;</span>), (<span class="string">&#39;L&#39;</span>, <span class="string">&#39;S&#39;</span>), (<span class="string">&#39;c&#39;</span>, <span class="string">&#39;f&#39;</span>),
         ]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;A&#39;</span>, <span class="string">&#39;J&#39;</span>), (<span class="string">&#39;L&#39;</span>, <span class="string">&#39;S&#39;</span>),
             (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;j&#39;</span>), (<span class="string">&#39;l&#39;</span>, <span class="string">&#39;s&#39;</span>),
             (<span class="string">&#39;\u{17F}&#39;</span>, <span class="string">&#39;\u{17F}&#39;</span>),
         ]));

         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;C&#39;</span>, <span class="string">b&#39;F&#39;</span>), (<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;G&#39;</span>), (<span class="string">b&#39;D&#39;</span>, <span class="string">b&#39;J&#39;</span>), (<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;C&#39;</span>),
             (<span class="string">b&#39;M&#39;</span>, <span class="string">b&#39;P&#39;</span>), (<span class="string">b&#39;L&#39;</span>, <span class="string">b&#39;S&#39;</span>), (<span class="string">b&#39;c&#39;</span>, <span class="string">b&#39;f&#39;</span>),
         ]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;J&#39;</span>), (<span class="string">b&#39;L&#39;</span>, <span class="string">b&#39;S&#39;</span>),
             (<span class="string">b&#39;a&#39;</span>, <span class="string">b&#39;j&#39;</span>), (<span class="string">b&#39;l&#39;</span>, <span class="string">b&#39;s&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_fold_az</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;A&#39;</span>, <span class="string">&#39;Z&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;A&#39;</span>, <span class="string">&#39;Z&#39;</span>), (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;z&#39;</span>),
             (<span class="string">&#39;\u{17F}&#39;</span>, <span class="string">&#39;\u{17F}&#39;</span>),
             (<span class="string">&#39;\u{212A}&#39;</span>, <span class="string">&#39;\u{212A}&#39;</span>),
         ]));
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;a&#39;</span>, <span class="string">&#39;z&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;A&#39;</span>, <span class="string">&#39;Z&#39;</span>), (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;z&#39;</span>),
             (<span class="string">&#39;\u{17F}&#39;</span>, <span class="string">&#39;\u{17F}&#39;</span>),
             (<span class="string">&#39;\u{212A}&#39;</span>, <span class="string">&#39;\u{212A}&#39;</span>),
         ]));

         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;Z&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;Z&#39;</span>), (<span class="string">b&#39;a&#39;</span>, <span class="string">b&#39;z&#39;</span>),
         ]));
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;a&#39;</span>, <span class="string">b&#39;z&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;Z&#39;</span>), (<span class="string">b&#39;a&#39;</span>, <span class="string">b&#39;z&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_fold_a_underscore</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;A&#39;</span>, <span class="string">&#39;A&#39;</span>), (<span class="string">&#39;_&#39;</span>, <span class="string">&#39;_&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">canonicalize</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;A&#39;</span>, <span class="string">&#39;A&#39;</span>), (<span class="string">&#39;_&#39;</span>, <span class="string">&#39;_&#39;</span>),
         ]));
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;A&#39;</span>, <span class="string">&#39;A&#39;</span>), (<span class="string">&#39;_&#39;</span>, <span class="string">&#39;_&#39;</span>), (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;a&#39;</span>),
         ]));

         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;A&#39;</span>), (<span class="string">b&#39;_&#39;</span>, <span class="string">b&#39;_&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">canonicalize</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;A&#39;</span>), (<span class="string">b&#39;_&#39;</span>, <span class="string">b&#39;_&#39;</span>),
         ]));
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;A&#39;</span>), (<span class="string">b&#39;_&#39;</span>, <span class="string">b&#39;_&#39;</span>), (<span class="string">b&#39;a&#39;</span>, <span class="string">b&#39;a&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_fold_a_equals</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;A&#39;</span>, <span class="string">&#39;A&#39;</span>), (<span class="string">&#39;=&#39;</span>, <span class="string">&#39;=&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">canonicalize</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;=&#39;</span>, <span class="string">&#39;=&#39;</span>), (<span class="string">&#39;A&#39;</span>, <span class="string">&#39;A&#39;</span>),
         ]));
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;=&#39;</span>, <span class="string">&#39;=&#39;</span>), (<span class="string">&#39;A&#39;</span>, <span class="string">&#39;A&#39;</span>), (<span class="string">&#39;a&#39;</span>, <span class="string">&#39;a&#39;</span>),
         ]));

         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;A&#39;</span>), (<span class="string">b&#39;=&#39;</span>, <span class="string">b&#39;=&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">canonicalize</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;=&#39;</span>, <span class="string">b&#39;=&#39;</span>), (<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;A&#39;</span>),
         ]));
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;=&#39;</span>, <span class="string">b&#39;=&#39;</span>), (<span class="string">b&#39;A&#39;</span>, <span class="string">b&#39;A&#39;</span>), (<span class="string">b&#39;a&#39;</span>, <span class="string">b&#39;a&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_fold_no_folding_needed</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\x10&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;\x10&#39;</span>),
         ]));

         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;\x00&#39;</span>, <span class="string">b&#39;\x10&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;\x00&#39;</span>, <span class="string">b&#39;\x10&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_fold_negated</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;x&#39;</span>, <span class="string">&#39;x&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">case_fold</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;X&#39;</span>, <span class="string">&#39;X&#39;</span>), (<span class="string">&#39;x&#39;</span>, <span class="string">&#39;x&#39;</span>),
         ]));
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>().<span class="ident">negate</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;\x00&#39;</span>, <span class="string">&#39;W&#39;</span>), (<span class="string">&#39;Y&#39;</span>, <span class="string">&#39;w&#39;</span>), (<span class="string">&#39;y&#39;</span>, <span class="string">&#39;\u{10FFFF}&#39;</span>),
         ]));

         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;x&#39;</span>, <span class="string">b&#39;x&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">case_fold</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;X&#39;</span>, <span class="string">b&#39;X&#39;</span>), (<span class="string">b&#39;x&#39;</span>, <span class="string">b&#39;x&#39;</span>),
         ]));
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>().<span class="ident">negate</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;\x00&#39;</span>, <span class="string">b&#39;W&#39;</span>), (<span class="string">b&#39;Y&#39;</span>, <span class="string">b&#39;w&#39;</span>), (<span class="string">b&#39;y&#39;</span>, <span class="string">b&#39;\xff&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_fold_single_to_multiple</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;k&#39;</span>, <span class="string">&#39;k&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">&#39;K&#39;</span>, <span class="string">&#39;K&#39;</span>), (<span class="string">&#39;k&#39;</span>, <span class="string">&#39;k&#39;</span>), (<span class="string">&#39;\u{212A}&#39;</span>, <span class="string">&#39;\u{212A}&#39;</span>),
         ]));

         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;k&#39;</span>, <span class="string">b&#39;k&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[
             (<span class="string">b&#39;K&#39;</span>, <span class="string">b&#39;K&#39;</span>), (<span class="string">b&#39;k&#39;</span>, <span class="string">b&#39;k&#39;</span>),
         ]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">class_fold_at</span>() {
         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;@&#39;</span>, <span class="string">&#39;@&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">canonicalize</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;@&#39;</span>, <span class="string">&#39;@&#39;</span>)]));
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">class</span>(<span class="kw-2">&amp;</span>[(<span class="string">&#39;@&#39;</span>, <span class="string">&#39;@&#39;</span>)]));

         <span class="kw">let</span> <span class="ident">cls</span> <span class="op">=</span> <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;@&#39;</span>, <span class="string">b&#39;@&#39;</span>)]);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">clone</span>().<span class="ident">canonicalize</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;@&#39;</span>, <span class="string">b&#39;@&#39;</span>)]));
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">cls</span>.<span class="ident">case_fold</span>(), <span class="ident">bclass</span>(<span class="kw-2">&amp;</span>[(<span class="string">b&#39;@&#39;</span>, <span class="string">b&#39;@&#39;</span>)]));
     }

     <span class="attribute">#[<span class="ident">test</span>]</span>
     <span class="kw">fn</span> <span class="ident">roundtrip_class_hypen</span>() {
         <span class="kw">let</span> <span class="ident">expr</span> <span class="op">=</span> <span class="ident">e</span>(<span class="string">&quot;[-./]&quot;</span>);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="string">&quot;(?u:[-\\.-/])&quot;</span>, <span class="ident">expr</span>.<span class="ident">to_string</span>());

         <span class="kw">let</span> <span class="ident">expr</span> <span class="op">=</span> <span class="ident">e</span>(<span class="string">&quot;(?-u)[-./]&quot;</span>);
         <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="string">&quot;(?-u:[-\\.-/])&quot;</span>, <span class="ident">expr</span>.<span class="ident">to_string</span>());
     }
 }
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