RE: Abbreviated Location Paths...

Subject: RE: Abbreviated Location Paths...
From: Kay Michael <Michael.Kay@xxxxxxx>
Date: Thu, 22 Apr 1999 10:55:48 +0100
> Jason Diamond [mailto:jason@xxxxxxxxxxxxx] wrote
> 
> On the other hand, I couldn't find any explanation nor was I able to
justify one
> on my own for the distinctions between expressions and patterns. Is this
purely
> an implementation issue or am I missing something?

I don't think it's just an implementation issue, I've been trying to figure
it out myself. As far as I can see (see last few paras before section 6.1):

- every pattern is an expression and its result type is always "node-set"
- Not every expression of type "node-set" is a pattern. But the only example
I have found that isn't is a docref().
- every location path is an expression
- every location path "that meets certain restrictions" is a pattern: I
haven't discovered what the restrictions are, nor have I discovered a use
for location paths that are not patterns
- every pattern (syntax rule 48) is either a location path or a union of
location paths

Answering your question, a pattern is one kind of expression. There are
syntactic contexts where the only kind of expression you can use is a
pattern, e.g. in the match attribute of <xsl:template>.

Mike Kay 


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