well,
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Von: Robert P. J. Day
Gesendet: Samstag, 23. August 2003 17:42
An: 'xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com'
Betreff: Re: AW: [xsl] 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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