Code that edits XML documents

Hi,

I need to implement a program that modifies an XML file, this file will
frequently also be edited by hand in a plain text editor. Of course, it's
important that the program does not remove or undo any of the hand-edited
changes (xml data, comments or whitespace). I have previously used Xerces
for reading XML.

What library can you recommend for editing/writing XML data? Can Xerces or
some addon do this? Is there anything in the JDK that I missed? Is there
another Apache project for this?

I'm looking for something that is simple, open source and java. Ideally I
would like something that works like this:

void updateXmlTagContent(Sometype document,
                         String xpathSayingWhichTagToUpdate,
                         String newTagContent);

Have anyone seen a library or tool that does this or something similar? It
doesnt have to be based on xpath, any solution that gets the XML document
updated will do.


rgrds,
martin