<!-- Element names -->
<!ENTITY % Doctype   "article">
<!ENTITY % Front     "front">
<!ENTITY % Body      "body">
<!ENTITY % Back      "back">
<!ENTITY % Title     "title">
<!ENTITY % Author    "author">
<!ENTITY % Date      "date">
<!ENTITY % Publisher "publisher">
<!ENTITY % Copyright "copyright">
<!ENTITY % Part      "part">
<!ENTITY % Paragraph "paragraph">
<!ENTITY % Number    "number">
<!ENTITY % Notes     "notes">
<!ENTITY % Appendix  "appendix">
<!-- Content substitutions -->
<!ENTITY % %Front;   "(%Title;, %Author;, %Date;, %Publisher;?, %Copyright;?)">
<!ENTITY % %Body;    "(%Part;+|%Paragraph;+)">
<!ENTITY % %Part;    "(%Number;?,%Title;?,%Paragraph;+)">
<!ENTITY % %Back;    "(%Notes;, %Appendix;*) | (%Appendix;*)">
<!ENTITY % block     "(%front;, %body;, %back;)">
<!-- Document Root -->
<!ELEMENT %Doctype; ( %block; )>
<!-- Document Front Matter -->
<!ELEMENT %Title; (#PCDATA)>
<!ELEMENT %Author; (#PCDATA)>
<!ELEMENT %Date; (#PCDATA)>
<!ELEMENT %Publisher; (#PCDATA)>
<!ELEMENT %Copyright; (#PCDATA)>
<!-- Document Body -->
<!ELEMENT %Part; (%part;)>
<!ELEMENT %Number; (#PCDATA)>
<!ELEMENT %Paragraph; (#PCDATA)>
<!-- Document Back Matter -->
<!ELEMENT %Notes; (%Paragraph;)+>
<!ELEMENT %Appendix; (%part;)>

Note: Fragment for illustration purposes only