| <!ELEMENT book (title, author+, section+)> | |
| <!ELEMENT title (#PCDATA)> | |
| <!ELEMENT author (#PCDATA)> | |
| <!ELEMENT section (title, (p | figure | section)* )> | |
| <!ATTLIST section | |
| id ID #IMPLIED | |
| difficulty CDATA #IMPLIED> | |
| <!ELEMENT p (#PCDATA)> | |
| <!ELEMENT figure (title, image)> | |
| <!ATTLIST figure | |
| width CDATA #REQUIRED | |
| height CDATA #REQUIRED > | |
| <!ELEMENT image EMPTY> | |
| <!ATTLIST image | |
| source CDATA #REQUIRED > |