InitializeXMLParser[root, "file"] creates an XMLParser object that has a list of entities corresponding to the contents of "file" and can be used on XML documents that have a root element root.
To use InitializeXMLParser, you first need to load the XML Package using Needs["XML`"].
InitializeXMLParser can be used to preload a DTD. If many documents with the same DTD are to be loaded repeatedly, a pre-initialized parser can speed up processing time.