Re: AW: why is "(chapter//footnote)[1]" illegal?

"Robert P. J. Day" <rpjday@xxxxxxxxxxxxxx> wrote in message
news:Pine.LNX.4.44.0308231135200.2185-100000@xxxxxxxxxxxxxxxxxxxxxxxx
> 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)

This is not a valid match pattern.

>   (chapter//footnote)[1] no (kay, 443)
>   ($chapters//diagram)[1] yes (kay, 355)

This is not a valid match pattern -- a match pattern should not contain a
reference to an xsl:variable.

I do not have the second edition of the book. Can't find any such examples
in the first edition.

>
> 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. :-)


As pointed above, your confusion stems from wrong understanding about the
validity of the above XPath expressions as match patterns.


=====
Cheers,

Dimitre Novatchev.
http://fxsl.sourceforge.net/ -- the home of FXSL




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