Example DTD
<!ELEMENT paper(author*, date, abstract?, body>
<!ATTLIST paper keywords CDATA #IMPLIED>
<!ELEMENT author(affiliation?, email, pcmember?)>
<!ATTLIST author name CDATA #REQUIRED>
<!ELEMENT affiliation (#PCDATA)>
<!ELEMENT email (#PCDATA)>
<!ELEMENT pcmember EMPTY>
<!ELEMENT abstract (p*|#PCDATA)>
<!ELEMENT body (section*)>
<!ELEMENT section (heading, (p|fig|section)*)>
<!ELEMENT p ((b|ref|#PCDATA)*)>
<!ATTLIST ref name IDREF #REQUIRED>
<!ATTLIST fig caption CDATA #IMPLIED>