Use DocumentElement to access the root node of the XML document. Because XML documents are hierarchical in structure, DocumentElement is the entry point to all data in the XML document. Setting DocumentElement replaces the entire data hierarchy with a new hierarchy of nodes. 

The IXMLNode interface includes properties and methods for examining and changing the text and attributes of a node, for adding and deleting child nodes, and for traversing the hierarchy of nodes rooted at that node. 

DOMDocument 

ChildNodes