( string str )
The function parses the XML document in str and
returns a tree PHP objects as the parsed document.
This function is isolated from the other functions, which means you cannot
access the tree with any of the other functions.
Modifying it, for example by adding nodes, makes no sense since there
is currently no way to dump it as an XML file.
However this function may be valuable if you want to read a file and
investigate the content.