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CORRECTION! (was Re: Assignment no, dynamic scoping si (was: Re: RE: Wishes for XSL revisions ...)
- From: "Evan Lenz" <elenz at xyzfind dot com>
- To: <xsl-list at lists dot mulberrytech dot com>
- Date: Wed, 2 Jan 2002 14:12:24 -0800
- Subject: [xsl] CORRECTION! (was Re: Assignment no, dynamic scoping si (was: Re: RE: Wishes for XSL revisions ...)
- Reply-to: xsl-list at lists dot mulberrytech dot com
Doh! My general statement was correct, but my example was wrong. So,
Wendell, sorry to mislead you, but your example in fact was wrong too!
I wrote:
> Unless a predicate is bound (without intervening parentheses) to
> a node test, it is always evaluated with respect to a "forward"
> axis (the XPath spec arbitrarily chooses the child axis).
So far, so good.
> ancestor-or-self::*[@source][last()]
>
> Your example features both kinds of predicates.
Oops. No, *both* predicates in the above example are tightly bound to the
node test (and thus the reverse axis), because the Step production is as
follows:
[4] Step ::= AxisSpecifier NodeTest Predicate*
| AbbreviatedStep
where the Step itself may have more than one predicate. So [last()] will
select the last node in *reverse* document order (or first in document
order), not the other way around! To get the intended result (getting the
"closest" ancestor), you would either write:
ancestor-or-self::*[@source][1]
or
(ancestor-or-self::*[@source])[last()]
In this second example, the [last()] predicate is no longer tightly bound to
the node test as part of the Step production; the parentheses render it as a
predicate of the second kind--as part of the FilterExpr production:
[20] FilterExpr ::= PrimaryExpr
| FilterExpr Predicate
And thus [last()] is applied to the result of the expression to the left
with respect to document order, selecting the last node in document order.
Multiple predicates in a reverse step with the last being positional--that
has got to rank pretty highly on the confuse-the-experts list of XPath
expressions.
Evan
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