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   RE: [xml-dev] Processing instruction guidelines

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> I'm trying to put together some guidelines about when we 
> should use processing instructions and when some other 
> construct (e.g. empty element, namespaced attribute) to pass 
> information to an application.
> Are there any other good uses for PIs? 

I use processing-instructions as follows, and I'm really not sure in my
own mind whether it's a good idea or not.

If I want a section of a document to contain a table of contents, I


and if I want it to contain a glossary, I write


These are instructions to the stylesheet to compute the appropriate text
and rendition time, so if "processing instructions" are intended as
instructions for processing, their use seems appropriate here.

I could have used an empty element, but then the DTD would have to know
about it. The stylesheet is under my control, but the DTD isn't. Am I
just bypassing the constraints that the DTD is trying to impose? I'm not
sure. There is a sense in which these PIs are not adding anything to the
information content of the document, they are only rendition hints.

I fall back on Tim Bray's mantra (sorry if I'm misrepresenting it) that
XML is just syntax, and you can therefore use it any way you like.

Michael Kay
Software AG
home: Michael.H.Kay@ntlworld.com
work: Michael.Kay@softwareag.com 


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