equivalence of <i><b></b></i> and <b><i></i></b> et. al. ?

I have written a natural language modelling tool which marks up (inserts 
XML tags into) natural language documents already in XML.

I have come across an issue with this tool: some users and documents 
have an expectation that <i><b></b></i> and <b><i></i></b> (and similar 
classes of constructs) are equivalent, whereas my tool sees these are 
completely distinct.

 From looking at at the standards, is appears that HTML, XHTML and XML 
are all silent on the semantics of situations such as this.

Are there any systems or toolkits which have already been written to 
help systematise documents and corpora into a single, consistent 
representation?

cheers
stuart

-- 
Stuart Yeates            
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