well,

> ----------
> Von: 	Robert P. J. Day
> Gesendet: 	Samstag, 23. August 2003 17:42
> An: 	'xsl-list@xxxxxxxxxxxxxxxxxxxxxx'
> Betreff: 	Re: AW:  why is "(chapter//footnote)[1]" illegal?
> 
> On Sat, 23 Aug 2003, Markus Abt wrote:
> 
> > Hi Robert,
> > 
> > a pattern (p.443) is a path expression, but not every
> > path expression (.p408) is a valid pattern.
> 
> well, since mom is still putzing around in the kitchen and not
> ready to go shopping yet, i'll expand on this a bit more.
> 
> i'm aware (kay, p. 430 -- a book that is getting mighty dog-eared by now)
> that "every pattern is a valid XPath expression, but not every valid XPath
> expression is a valid pattern." fair enough -- kay uses the example of
> "2+2" as an expression that makes no sense as a pattern.
> 
> but that example is pretty obvious -- "2+2" *clearly* can't be
> interpreted as a pattern.  it's not so obvious why the following
> set of expressions can or can't be used as patterns:
> 
>   (chapter/para)[1]		yes (kay, 408)
>   (chapter//footnote)[1]	no (kay, 443)
>   ($chapters//diagram)[1]	yes (kay, 355)

(chapter/para)[1]		no
(chapter//footnote)[1]	no
($chapters//diagram)[1]	no

All three can not be used as patterns.

> it's not at all clear *intuitively* why the first and third expressions
> are acceptable patterns, while the second isn't.  and it's not because
> that 2nd expression couldn't be interpreted unambiguously, AFAICT.
> 
> after i take a closer look at the actual rules for acceptable patterns,
> i'm sure i'll understand it.  but i just won't like it. :-)
> 
> rday
> 

Markus
__________________________
Markus Abt
Comet Computer GmbH
http://www.comet.de



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