Fragment of NPAC Education XML DTD
<!ELEMENT npaceducationxml (quiz+, lecture+, author+, course+) >
<!ELEMENT quiz (question)+>
<!ATTLIST quiz quizID ID #REQUIRED
lectureID IDREF #REQUIRED>
<!ELEMENT author (name, email+, institution)>
<!ATTLIST author authorID ID #REQUIRED>
<!ELEMENT name (family, given)>
<!ELEMENT family (#PCDATA)>
<!ELEMENT given (#PCDATA)>
<!ELEMENT email (#PCDATA)>
<!ELEMENT institution (#PCDATA)>