You've somehow got it into your head that the context for evaluation of the rh
operand depends on the lh operand. Like I said, you're thinking of it as a
predicate. That's not the case.
descendant::* except self::heading
must be wrong, because the descendant axis never includes a node that's on the
self axis: this is like saying "all my descendants except myself".
Michael Kay
Saxonica
On 2 Feb 2014, at 21:50, Graydon <graydon(_at_)marost(_dot_)ca> wrote:
On Sun, Feb 02, 2014 at 09:04:28PM +0000, Michael Kay scripsit:
Perhaps you are reading "except" as "that are not", i.e. a negated
predicate rather than a set difference). In English this reading would
often work, as in "all vehicles that are not bicycles". But in English
grammar, what follows "except" is not a predicate that qualifies what
precedes it: you cannot say "all vehicles except blue". So I think the
XPath usage is aligned with English usage in this instance.
I've found it useful to read "except" as "without"; I have a sequence,
and what I get is that sequence without the members of this other
sequence which I get to define.
The place I usually get snarled up is remembering that the sequences
are.
* except heading
is easy, that's "all the element children without any heading children",
(child::*) except (child::heading)
* except (heading, references)
is easy, that's "all the element children without any members of this
thing that's really a sequence which happens to be defined as heading or
reference elements",
(child::*) except (child::heading,child::references)
descendant::* except heading
is really "all the descendant elements without any child heading
elements of the context node", and that's usually a source of
intractable bugs. I think it should be
descendant::* except self::heading
if I want all the descendant elements without any of the descendant
elements who happen to be heading elements.
But then in XSLT 3.0 (at least as currently available) I can say
<xsl:template match="descendant::* except self::heading">
<!-- something happens -->
</xsl:template>
and I get lost because I have no idea how the first sequence is defined.
-- Graydon
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