SAX2: Namespace Processing and NSUtils helper class

[David Brownell]

james anderson wrote:
> 
> i had understood
>   {"","a",""},
> from the example, to denote a name in a namespace for which there would have
> been a declaration, namely a binding such as
> 
>   <... xmlns="" ... >
> 
> for the ignominious "null" namespace. how does this come to correspond to
> 
>   { undeclared, "a", valid-prefix } ?

It doesn't.  Namespace URIs clearly have three kinds of values, not that
it's specified in the namespace spec very clearly (and I suspect DOM L2
may need tweaking to get this right):

	- Undeclared (null?)
	- Declared as no-value (empty string, "")
	- Some URI (the case folk focus on).

The distinction between "undefined" and "empty" will be familiar to folk
in the database world (maybe with different terms).  SAX2 will have to be
clear on how it exposes this.

One more edge case for applications to trip over!

- Dave



> i agree that an "==" implementation needs to account for this, but didn't
> think it was nonconformant.
> 
> David Brownell wrote:
> >
> > David Megginson wrote:
> > >
> > > Clark C. Evans writes:
> > >
> > >  > On Sun, 26 Dec 1999 uche.ogbuji at fourthought.com wrote:
> > >  > >
> > >  > > {"http://www.w3.org/1999/xhtml", "a", ""} ==
> > >  > > {"http://www.w3.org/1999/xhtml", "a", "html"}.
> > >  >
> > >  >          {"","a",""} != {"","a","html"}
> > >
> > > As I understood it, the suggestion was that
> > >
> > >   {"", "a", ""} == {"", "a", "html"}
> >
> > Actually I think the namespace spec defines
> >
> >     { undeclared, "a", valid-prefix }
> >
> > as "namespace-nonconformant", AKA some kind of error which they
> > neglected to describe well enough to support portable APIs.
> >
> > Meaning that any application choosing to use such a "Name"
> > class (which IMHO is a fine notion) needs to treat this value
> > with care ... IEEE floating point math has a variety of sorts
> > of "NaN" values, perhaps useful models can be found there.
> > I'd suggest that most "==" tests against such a Name ought to
> > fail, and ordering tests should cause exceptions.
> >
> 
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