XDNL XML DTD
http://www.w3.org/TR/xdnl/

             <!ENTITY % char-instructions "
               | xdnl:for-each
               | xdnl:value-of
               | xdnl:text
               | xdnl:copy-of">

             <!ENTITY % instructions "
               %char-instructions;
               | xdnl:link
               | xdnl:processing-instruction
               | xdnl:comment
               | xdnl:element
               | xdnl:attribute">

             <!ENTITY % char-template "(#PCDATA  %char-instructions;)*">

             <!ENTITY % template "(#PCDATA  %instructions;)*">

             <!ENTITY % expr "CDATA">

             <!ENTITY % avt "CDATA">

             <!ENTITY % URI "CDATA">

             <!ENTITY % num "CDATA">

             <!ENTITY % type "CDATA">

             <!ENTITY % chunk-type "CDATA">
             <!-- head, tail, series, 1,2,4-6 -->

             <!ENTITY % term-string "CDATA"><!-- ... -->

             <!ENTITY % chunk-atts '
               chunk-size %num; #IMPLIED
               chunk %chunk-type; #IMPLIED
               termination-string %term-string; #IMPLIED'>

             <!ENTITY % counter-atts '
               counter-size %num; #IMPLIED
               chunk %chunk-type; #IMPLIED'>

             <!ELEMENT   xdnl:documents (xdnl:leaf-document)* >

             <!ELEMENT   xdnl:leaf-document %template; >
             <!ATTLIST xdnl:leaf-document
               select %expr; #REQUIRED
               type   %type; #REQUIRED>

             <!ELEMENT xdnl:copy-of %template;>
             <!ATTLIST xdnl:copy-of
               select %expr; #REQUIRED
               %chunk-atts;>

             <!ELEMENT xdnl:value-of EMPTY>
             <!ATTLIST xdnl:value-of
               select %expr; #REQUIRED
               %chunk-atts;>

             <!ELEMENT xdnl:for-each %template;>
             <!ATTLIST xdnl:for-each
               select %expr; #REQUIRED
               condition %expr; #IMPLIED
               %counter-atts;>

             <!ELEMENT xdnl:link %template;>
             <!ATTLIST xdnl:link
               href %URI; #REQUIRED
               %chunk-atts;>

             <!ELEMENT xdnl:element %template;>
             <!ATTLIST xdnl:element
               name %avt; #REQUIRED
               %chunk-atts;>

             <!ELEMENT xdnl:attribute %char-template;>
             <!ATTLIST xdnl:attribute
               name %avt; #REQUIRED>

             <!ELEMENT xdnl:text (#PCDATA)>

             <!ELEMENT xdnl:processing-instruction %char-template;>
             <!ATTLIST xdnl:processing-instruction  name %avt; #REQUIRED>

             <!ELEMENT xdnl:comment %char-template;>