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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.