Each document has a DOCTYPE attribute that whose value is either null or a DocumentType object.
The DocumentType object provides an interface to the entities defined for an XML document.
|entities||Returns a NamedNodeMap containing the entities declared in the DTD|
|internalSubset||Returns the internal DTD as a string|
|name||Returns the name of the DTD|
|notations||Returns a NamedNodeMap containing the notations declared in the DTD|
|systemId||Returns the system identifier of the external DTD|