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   xpath union and node set order

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Hi, I'm looking for an answer to this question:

Am I right in saying that both these paths should return nodes in the
same order?


on this document:

and that the order should be the document order:

Or is the order something I can't count on?

I'm using a DOM, and xpath through the msxml-like interface method
IDomNodeSelect.selectNodes. And that particular DOM returns the node set for
"//c|b" in this order:

I found a couple of things in the spec that may be relevant, listed below.
[2] says the node set is unordered, so it is implementation dependent. [1]
and [3] are very specific on document order - [1] when used with a
predicate, [2] regarding proximity position.

Is there a difference between the finally resulting node set and the node
set in the expression? I would think the resulting node set should be like
the second part of the example in [1], using the child axis, and in document

[4] says I have to specify an ordered node set, or I will get an unordered
on. IDomNodeSelect.selectNodes does not follow [4], but it does suggest that
I can't rely on document order.

With [1] and [3] being very specific about document order, I get the
impression that it it allowed to scramble the node set order before
delivering the results ;-)

I based some code on the assumption that I would always get document order.
If I'm right, I'll file a bug report for the DOM, and maybe fix it. If not,
my code is rather flawed. I'll have to fix either the DOM or my code...


Bits from the spec (http://www.w3.org/TR/xpath):

[1] Section 3.3
The meaning of a Predicate depends crucially on which axis applies. For
example, preceding::foo[1] returns the first foo element in reverse document
order, because the axis that applies to the [1] predicate is the preceding
axis; by contrast, (preceding::foo)[1] returns the first foo element in
document order, because the axis that applies to the [1] predicate is the
child axis.

[2] Section 1
node-set (an unordered collection of nodes without duplicates)

[3] Section 2.4
The proximity position of a member of a node-set with respect to an axis is
defined to be the position of the node in the node-set ordered in document
order if the axis is a forward axis and ordered in reverse document order if
the axis is a reverse axis.

And from DOM Level 3 XPath
[4] Section 1.4
If the natural result is a node set when ANY_TYPE was requested, then
UNORDERED_NODE_ITERATOR_TYPE is always the resulting type. Any other
representation of a node set must be explicitly requested.


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