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 issue 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 node-set/sequence in reverse document order? what's the plain English definition of a sequence then (as apposed to the mathematical explanation)? 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 Can I conclude that Evans explanation is no longer applicable in xpath 2.0, since I can't find an expression of the second form anywhere in the spec?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 system. 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
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