Re: How to match on namespace prefix

[Chris Lilley <chris@xxxxxx>]

Francois Belanger wrote:
> 
> James Clark wrote on 04/01/99 19h16:

> >Issue (pattern-namespace-wildcards): Should patterns of the form foo:*
> >or *:foo be allowed?
> 
> Yes, it's really needed, so is @*:foo or @foo:* for attributes, the
> syntax is simple and intuitive.

No, it should not be allowed.

However, the probelem that the proposal is trying to solve should be
solved.

In CSS, solutions of the form 

@namespace foo url(someurlgoeshere);

foo:X { font-style: italic}

are being considered, which given the instance

<xyz xmlns:bar='someurlgoeshere' xmlns:foo='adifferenturl'>
  <bar:X>this element is in italics</bar:X>
  <foo:X>This one is not</foo:X>
</xyz>

would match bar:Xm in other words the one from the correct namespace.
(It might be that we pick a different separator that : which is
currently not legal in a selector unless escaped.)

The key point here is that equality is beased on the declared namespace
*name*, not the namespace *prefix* which happend to be used in a
particular instance. This increases the robustness of the style sheet
and allows it to be applied to content which happens, for some good
reason, to use a different namespace prefix. It also stops unwanted
selection of unrelated elements from a diufferent namespace, that happen
to use the same namespace prefix.

It would be desirable for the XSL solution to exhibit a similar
robustness. An appropriate XML construct would be used to replace the
at-rule.

In the CSS WG we discussed making the @namespace a block container but
found that this precluded contextual selectors that use multiple
namespaces (select all elements Q from namespace w that are children of
element A from namespace s).


> >If so, should * match any element or any element
> >without a namespace URI?
> 
> * should match any nodes (it's what one expects).  I would expect to
> write *:* if I want all nodes who are part of any namespace. 

This problem goes away if matching is via the  namespace name. In the
CSS example above, foo:X matches elements called X from the namespace
declared by 'someurlgoeshere' regardless of whether the elements in the
document instance are prefixed with a namespace prefix or whether they
are in the default namespace (ie have no prefix).

So * matches all elements in all namespaces. foo:* matches all elements
in the namespace declared by 'someurlgoeshere' (regardless of whether
they happen to have an explicit namespace prefix in the document
instance) and *:X matches all elements called X in all namespaces.

--
Chris



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