The DOMDocumentType class
Each DOMDocument has a doctype attribute whose value is either NULL or a DOMDocumentType object.
The public identifier of the external subset.
The system identifier of the external subset. This may be an absolute URI or not.
The name of DTD; i.e., the name immediately following the DOCTYPE keyword.
A DOMNamedNodeMap containing the general entities, both external and internal, declared in the DTD.
A DOMNamedNodeMap containing the notations declared in the DTD.
The internal subset as a string, or null if there is none. This is does not contain the delimiting square brackets.