Why not PIs for namespace declarations?

Arjun Ray aray at q2.net
Sat Dec 25 04:31:09 GMT 1999

On Fri, 24 Dec 1999, james anderson wrote:
> Arjun Ray wrote:
> > On Thu, 23 Dec 1999, David Brownell wrote:

> > The "requirement" that had to be met, apparently, was that the
> > syntactic device announcing a "local" lexical scope had to be 
> > "locally" available itself (thus ruling out, e.g., stuff in the
> > internal subset that would be indefinitely "far away".)
> I surmise that "stuff" here refers to a PI which would have preceeded
> or followed the respective element tag. 

Not just a PI.  ArchForms, for instance, work with attributes which have
to be declared in <!ATTLIST...> declarations.  (New-fangled PIs are one
way of working around the fact that declarations can't appear within the
instance.)  The *general* idea - to use "special" attributes - can be
considered well-accepted; the issue is how these special attributes are to
be recognized.

> > There are only two natural scoping constructs in XML: elements and
> > marked sections.  

> As XML had, to that point in time, neither a storage nor a processing
> model, any arguments regarding "natural" whould have been most
> suspect.

Natural in the syntactic sense: both "start" and "end" lexically separate
and explicit.  "Natural scoping constructs", not "natural scopes":)

> A claim, for example, that the present encoding does not place the
> encoding for the namespace binding "indefinitely far away" from the
> encoding for the respective element type depends on the presumption of
> a procesing structure akin to that proposed in the recent strawman
> sax2. Namely one in which interning the type name is deferred until
> the attributes have been read. A PI encoding with a lexical scope
> covering the immediately succeeding element would not have made this
> presumption.

Yes.  The inherent chicken-and-egg problem is normally solved by
separating declaration and use (and sometimes the declaration can be
"indefinitely far away" enough to have to be assumed - e.g. in some
block-structured languages, a new block *mandates* a new lexical scope, so
there's no need to "declare" this fact.)


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