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RE: [xsl] xpath trickery (was A Question **TO** XSLT Newbies)
Subject: RE: [xsl] xpath trickery (was A Question **TO** XSLT Newbies)|
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Fri, 25 Apr 2003 14:12:30 -0400
At 06:54 PM 4/24/2003, you wrote:
> - variable in XPath seem to be allowed / disallowed in random ways.
A variable is allowed in precisely the same places as you can use a
literal value or a function call. What is random about that?
Well, to be fair to Simon, they also can't appear in any XPath expression
being used as a match pattern.
In my experience disentangling this tight weave comes first from knowing
where the dividing line between XPath and XSLT is ... as well as knowing
where they depend on each other. E.g. that XPath leaves to its application
(viz. XSLT) -- the determination of things like context size and position
... hence troubles understanding what position() and last() actually do.
Only when you have a clear grounding on what XPath does as an expression
language does it become clearer why, for example, restrictions are placed
on XPath in some -- not all -- places in XSLT. (That is, what's a match
pattern and what's just XPath retrieving nodes.) This, in turn, requires a
good grasp of the XSLT processing model.
I thought Simon's list of what's confusing about XPath was an excellent
synopsis, and can only respond to him by recommending -- again -- that some
time spent going over XPath *without trying to solve a particular
problem!*, not only its syntax but (more importantly) its data model,
datatypes, functions (since not all functions in use in XSLT are in XPath!)
and (yes) casting rules -- is well worth it. If at all possible, with the
help of an expert. If you have some help disentangling it -- and
particularly if (as you say, Mike) you can avoid imposing mistaken notions
and theories based on experience with other technologies or ideas of
"should" -- it proves not to be all that hard after all.
Only time will tell whether this situation is bettered or worsened by XPath
Wendell Piez mailto:wapiez@xxxxxxxxxxxxxxxx
Mulberry Technologies, Inc. http://www.mulberrytech.com
17 West Jefferson Street Direct Phone: 301/315-9635
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