Re: [xml] Using Xpath with default namespace and null prefix

[Daniel Veillard <veillard redhat com>]

On Mon, Feb 08, 2010 at 01:14:22PM +0100, Iñaki Baz Castillo wrote:
> El Lunes, 8 de Febrero de 2010, Daniel Veillard escribió:
[...]
> Does it mean that Xpath 2.0 allows the behavior I meant (present in RFC 4825)?

  I don't know, I doubt it.

> Is it planned libxml2 to implement Xpath 2.0?

  I have no such plan

> > I also see it reference XML Fragment Interchange CR draft, so I really
> > wonder if the liaison work was properly done on that IETF specification >:->
>
> RFC 4825 is a pain as it reuses Xpath 1.0 with some restrictions and additions 
> (as the "application default namespace" which allows the Xpath deviation I 
> told) so a XML library implementing Xpath 1.0 is not enough valid to implement 
> a XCAP client/server :(

  You will have to capture the XPath expression and mofify them before
calling libxml2, there won't be any way around.

The fundamental reason why allowing something like "//foo" to mach an
element in the default namespace is that this namespace can change
wherever in the document

<foo>
 <foo xmlns="http://example1.com/foo"/>
 <foo xmlns="http://example2.com/foo"/>
</foo>

//foo would then returns 3 elements with completely different semantic
coming from different vocabularies. XML being designed for being
extensible XPath had to put a safeguard. Matching in XPath is designed
as a match on the tuple [Namespace URI name , element name] , that's
made 100% clear in the XPath spec, the prefix, present or not, is
completely irrelevant in the XPath query.

Daniel

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