"reference to undefined XML name" in E4X queries

[Massimiliano Mirra]

I've run into a major obstacle while trying to query mildly
heterogeneous XML datasets with E4X. The following works:

> var dataset = <dataset>
<entry type="normal"><foo/></entry>
<entry><bar/></entry>
</dataset>;
> dataset.entry[0].@type == 'normal'
true
> dataset.entry[1].@type == 'normal'
false

So, I could loop over the dataset using "for each", and
collect children having @type == "normal". But that seems silly,
since E4X has query capabilities, so I try:

> dataset.entry(@type == 'normal')
typein:19: ReferenceError: reference to undefined XML name @type

Hmmm.

Turns out that the latter behaviour is expected, more or less [1],
although I can't help but find it inconsistent with the former.

There is a workaround:

> dataset.entry(function::attribute('type') == 'normal')

But it quickly becomes unwieldy. For example, if you introduce
namespaces, instead of having:

> const myns = 'http://my.namespace.org'
> dataset.entry(@type == 'normal' && @myns::otherattr ==
'otherval')

You have:

> const myns = 'http://my.namespace.org'
> dataset.entry(function::attribute('type') == 'normal' &&
function::attribute(new QName(myns, 'otherattr))
== 'otherval')

At which point, switching to DOM and XPath suddendly starts looking
attractive...

The only relevant entry in bugzilla I found is
https://bugzilla.mozilla.org/show_bug.cgi?id=246441#c14. I'd be
grateful for opinions before possibly filing this by itself.

Massimiliano

[1] http://groups.google.com/group/netscape.public.mozilla.jseng/msg/1e756e711720e1c5