Use DOMDocument to directly access the IDOMDocument interface for the parsed XML document. This is the interface supported by the DOM parser for the document. 

Most applications do not need to use the DOMDocument property directly. Instead, it supplies the underlying support for parsing and manipulating the nodes accessed through DocumentElement. If you do want to make use of DOMDocument's low-level support, you must be familiar with the W3C Document Object Model (DOM) Specification. 

DocumentElement