
<!ELEMENT root ANY>
<!ELEMENT empty EMPTY>

<!-- 
  According to the spec, both 'pcdata' and 'mixed' here have "mixed content", but
  we'll use the term "pcdata" when only text nodes are allowed within an element.
-->
<!ELEMENT pcdata (#PCDATA)>
<!ELEMENT mixed (#PCDATA|empty|pcdata|mixed)*>

<!--
  All of the following have "children" content.  The productions are (neglecting 
  whitespace):
    children ::= (choice | seq) ('?' | '*' | '+')
    cp       ::= (Name | choice | seq) ('?' | '*' | '+')
    choice   ::= '(' cp ( '|' cp )* ')'
    seq      ::= '(' cp ( ',' cp )* ')'
-->
<!ELEMENT choice1 (chapter|appendix)+>
<!ELEMENT choice2 (chapter|appendix)?>
<!ELEMENT choice3 (chapter|appendix)*>
<!-- Nested choice -->
<!ELEMENT choice4 (chapter | (choice1 | choice2 | choice3)+)>

<!ELEMENT seq1 (chapter+, appendix+, glossary*)+>
<!ELEMENT seq2 (chapter+, (choice1 | choice2), (seq1, seq2?)+)?>

<!ELEMENT  chapter (#PCDATA)>
<!ELEMENT  appendix (#PCDATA)>
<!ELEMENT  glossary (#PCDATA)>

<!ELEMENT article (abstract?,(intro|preface),section+)?>