An example DTD file

<!ELEMENT div (head*, (lg|l|lb)*, signed*)>
<!ATTLIST div n  CDATA #IMPLIED
              type CDATA #IMPLIED> 
<!ELEMENT lg (head?, (l|lb)+)  >
<!ATTLIST lg n  CDATA #IMPLIED>
<!ELEMENT head (#PCDATA) >
<!ATTLIST head type  CDATA #IMPLIED>
<!ELEMENT l  (#PCDATA|emph|q|lb)* >
<!ELEMENT lb EMPTY >
<!ATTLIST lb n CDATA #IMPLIED>
<!ELEMENT q (#PCDATA|lb)*>
<!ELEMENT signed (#PCDATA)>
<!ENTITY mdash "&#x2014;">

This might be invoked using a DOCTYPE statement like the following

<!DOCTYPE div SYSTEM "filename.dtd" []>