XMLModifier offers an easy-to-use interface for users to
take advantage of the incremental update of VTD-XML
The XML modifier assumes there is a master document on which
the modification is applied: users can remove an element, update
a token, replace an element name, or insert new content anywhere in the document
transcoding methods are built-in
The process:
* The modification operations are recorded first
* The output() is called to generate output document