[xsl] RE: Postional predicates de-mystified

Subject: [xsl] RE: Postional predicates de-mystified
From: DPawson@xxxxxxxxxxx
Date: Fri, 4 Jan 2002 09:55:37 -0000
>  Evan Lenz wrote:

> The predicate in the second example is not part of the Step, 
> but is part of
> a more general FilterExpr. In XPath 1.0, a predicate may 
> follow any kind of
> expression; in this case, it follows a parenthesized expression. The
> parentheses render preceding::foo an expression in its own 
> right (without a
> predicate), yielding an opaque node-set. A node-set never retains
> information about what axis was used to select it. That 
> node-set result is
> subsequently filtered with a predicate. When a predicate applies to an
> expression, the XPath spec says, it is evaluated with respect 
> to the child
> axis. (The child axis is arbitrarily chosen because it's an 
> example of a
> forward axis.) Consequently, the predicate filters out all 
> nodes but the
> first node in *document order*.

Which seems to be the heart of the matter.
A quick scan of xpath 2.0 gives a count of node-set about 7 times (excluding
related occurences).

This word 'sequence' however, appears to occur slightly more times :-)

<quote>A sequence is an ordered collection of zero or more items. An item is
either a simple value or a node.</quote>

The 'order' mentioned here, is it document order or can I still collect a
in reverse document  order?
  what's the plain English definition of a sequence then (as apposed to the

and the FilterExpr has gone from 2.0. Indeed the filter only appears to be
mentioned with
respect to queries. Can I conclude that Evans explanation is no longer
in xpath 2.0, since I can't find an expression of the second form anywhere
in the spec?
(preceding::foo)[1] would now appear to be invalid.

Regards DaveP


NOTICE: The information contained in this email and any attachments is 
confidential and may be legally privileged. If you are not the 
intended recipient you are hereby notified that you must not use, 
disclose, distribute, copy, print or rely on this email's content. If 
you are not the intended recipient, please notify the sender 
immediately and then delete the email and any attachments from your 

RNIB has made strenuous efforts to ensure that emails and any 
attachments generated by its staff are free from viruses. However, it 
cannot accept any responsibility for any viruses which are 
transmitted. We therefore recommend you scan all attachments.

Please note that the statements and views expressed in this email 
and any attachments are those of the author and do not necessarily 
represent those of RNIB.

RNIB Registered Charity Number: 226227

Website: http://www.rnib.org.uk 

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list

Current Thread