Re: [xml-dev] Re: determining ID-ness in XML

[David Carlisle <davidc@nag.co.uk>]

> 1) They're not scoped, everything else about the language is.
Well a pi that declares an attribute to be of type ID may be compared to 
an attribute declaration doing the same, and attribute declarations
aren't really scoped (other than to the whole document) either.

> 2) They're not declared in the grammar (DTD/Schema), so their usage is not
> subject to any declarative/universal quality control:

That is surely a feature of the schema language rather than of PIs.
DTD's intentionally don't control pi's (or to put it another way pi's
are intentionally there to do things that are not constrained by the
grammar of the dtd) but a different schema language could easily choose
to have constraints on these. You (or at least the schema WG) choose not
to do so in W3C XML Schema, but you could have done so. Schematron
schemas for example can constrain the position and content of PIs (and
comments and anything else in the XPath data model).

David

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