This class represents a Document Type
declaraction in the document itself,
not a Document Type Definition (DTD). An XML document may (or may not) have such a reference.
DocumentType is an Extended DOM feature, used in XML documents but not in HTML.
Note that Entities and Notations are no longer children of the DocumentType, but are parentless nodes hung only in their appropriate NamedNodeMaps.
This area is UNDERSPECIFIED IN REC-DOM-Level-1-19981001 Most notably, absolutely no provision was made for storing and using Element and Attribute information. Nor was the linkage between Entities and Entity References nailed down solidly.
@version
@since PR-DOM-Level-1-19980818.