> I was thinking more of changing/losing some useful data - 

That's the catch, no one ever specifies that they throw away useful data,
but one person's usless dom padding white space, is another person's 
inter word space. 

> The only biggie I can think of is defaulted values - if the DTD
> changes and the new data doesn't keep the reference to the DTD then
> the new data won't reflect any changes in the defaulted values.


You can always get xsl:output to to stick a doctype back on.

> As an aside, from what you've just said, if the DTD expects a
> namespace declaration but that namespace is redundant and gets
> removed, the document would no longer validate after the identity
> transform (if the DTD was generated in the output).

yes, if you wrote a dtd that demands xmlns="" on every element
then process it through xslt identity transform you will get no xmlns=""
at all in the output. Tough:-) You can make it validate again by making
the dtd  default the namespace back.

David

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