[REBOL] Re: Rebol & XML
From: rebol:gavinmckenzie:fastmail:fm at: 8-Aug-2003 8:51
On Wed, 6 Aug 2003 15:03:10 +0200, "bryan" <[bry--itnisk--com]> said:
> >yeah I thought there might be problems, another problem is in the rare
> >occurrence of namespace prefixed attributes.
>
> Actually considering not too rare in cases of xml coming out of
> academia, or certain standards, where the xml namespace will be used,
> especially in example like following:
>
> <?xml version="1.0"?>
> <doc>
> <p xml:lang="EN">Good Morning!</p>
> <p xml:lang="EN-US">Howdy!</p>
> </doc>
>
> note that the xml namespace does not need to be declared anywhere.
>
Yeah, well the xml: namespace is special. It is implied. Though, there
is acually a formal namespace URI for the xml namespace, so it *is*
possible for it to be declared in an XML file. The xml namespace is only
used for xml:lang and xml:space though. It is illegal for people to use
this namespace other than for xml:lang and xml:space.
Besides the xml namespace, others will be declared. Namespaces are
tricky to implement in a parser/dom. The following snippets of XML are
equivalent, though their syntax differs greatly:
<a:a xmlns:a="whatever">
<b xmlns="something-else">text<b>
</a:a>
<a xmlns="whatever">
<b:b xmlns:b="something-else">text<b:b>
</a>
<a:a xmlns:a="whatever">
<a:b xmlns:a="something-else">text<a:b>
</a:a>
Note the nasty third example where the namespace prefix 'a' is redeclared
locally for the element scope of 'b'.
In short, for a namespace implementation the prefix: part of a namespace
is almost entirely useless. It would be incorrect or at least very
dangerous to build code that path-ed into an XML with an assumption about
the prefixes: e.g. it would be bad to write a path like xml/a:a/b:b
because the prefixes a: and b: are only present in one of the several
ways to encode the same XML above.
Gavin.
