Re: Questions on the new XSL spec (section 2.6)

[Steve Dahl <sdahl@xxxxxxxxxxx>]

James Clark wrote:

> Steve Dahl wrote:
> >
> > James Clark wrote:
> >
> > > ...
> > > 2.6.2 says:
> > >
> > > "[2] MatchExpr ::= SelectExpr
> > >
> > > A match pattern must match the production for MatchExpr; a node matches
> > > the match pattern if the MatchExpr returns true when evaluated
> > > with that node as context.
> > >
> > > The result of the MatchExpr is true if, for any node in the document
> > > that contains the context of the MatchExpr, the result of evaluating the
> > > SelectExpr with that node as context contains the context of the
> > > MatchExpr. Otherwise the result is false."
> >
> > Ah. Thanks. Rereading this passage clarified a lot.
>
> Your comments make me realize that the use of the word "contains" in
> that passage is ambiguous: "that contains" is qualifying "document" not
> "node in the document".  The second "contains" is talking about set
> containment.
>
> Is this clearer?
>
> The result of the MatchExpr is true if, for any node in the same
> document as the context of the MatchExpr, the set of nodes that results
> from evaluating the SelectExpr with that node as context has as one of
> its members the context of the MatchExpr. Otherwise the result is false.
>
> James

...and that's clearer yet. As a user of XSL, that was how I wanted it to be, but
as an implementor of an XSL processor, I could appreciate the performance
advantages of searching only the ancestors of the match candidate (and for most
patterns that's all you'd need to test anyway).

Thanks much for the explanations.



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