Hello Leigh Dodds is absolutely right in is "no silver bullet" message. What I had in mind is an answer to the problem raised by "Susan B. Farmer" <sfarmer@GOLDSWORD.COM> ... there was no way to take *this* file back into DELTA. But more than that; all of the continuous data in the original file (aka measurements) are now gone and will have to be added back into the DELTA data set by hand. :-( Why not extend the current standards that if there are data types that their particular application doesn't recognize, they stay around -- just ignored. So for the programmer it implies that the DOM model should be kept throughout the application program, and not be rewriten from scratch when the user pushes "save". About Leigh Dodds' example: <application-B-tag references="8"> I referred to standard chart X to finally decide on shapes. </application-B-tag> The 'references' attribute is like a pointer in C, or a foreign key in a database. The example's application B could have put its tag inside the concerned <character> element. In this case application A would logically destroy the comment of B together with with the character. Or another solution would be for the 'references' attribute to be an IDREF (XML's reference to a document-unique ID); in this way the DOM implementation would probably forbid the deletion of the element being referenced. Cheers JMV