I'm writing a XSLT that has to translate XML to plain ascii text. The XML contains unicode characters, possibly any of them. I cannot control the authoring so I must handle whatever is thrown at me.

I have a few dozen specially know character translations for things like 1/4 and degrees unicode symbols.
But I have a need to "catch all" charactors that are not mapped explicitly (rather then map explicitly the entiure unicode set) and translate them into something like "<UNKNOWN CHARACTER>"

Any suggestions on how to do this ? I could trivially write a post- processor to do this (maybe a dozen lines of C or java) but if there's a feature directly in XSLT I'd love to try that.

Any ideas welcome !