Points of influence in an XML Document

Has anyone developed any parsing strategies to handle location of fragments
within an XML document. I would suspect that most editors have something
like this built in. For example if the user changes some text (e.g. element
name) at a given line and column position is there a way to determine what
portion of the document is influenced? In many cases it is the containing
element and its children-- however I think that this could be further
optimized when the children have not changed (only changed position). Does
anyone have more information on this?

Thanks,
Jeff Rafter
Defined Systems
http://www.defined.net
XML Development and Developer Web Hosting