boning up on my predicates and patterns, i'm reading
kay, p. 443, which states:
"(chapter//footnote)[1] is not a valid pattern. (Why not?
No good reason, it's just that the spec doesn't allow it."
but on p. 408, there is an explanation of the (apparently
acceptable) path expression "(chapter/para)[1]".
so is it just the difference between using the child axis
and the descendant-or-self axis? it's not obvious to me
why the first should be illegal while the second is legal.
The syntax for patterns is a small subset of the syntax for XPath
expressions, and the subset doesn't allow parentheses.
The subset was chosen to make it easy for implementations to test
whether a node matches a pattern without going through the full
algorithm of evaluating the expression for every ancestor of the node
being tested.
Michael Kay
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