KH> foreign[(_at_)lang = ancestor::*[(_at_)lang][1]/@lang]
MK> foreign[(_at_)lang = (ancestor::*/@lang)[last()]]
These are equivalent.
(1) take the lang attribute of the first ancestor element (going upwards)
that has a lang attribute
(2) take all the lang attributes belonging to ancestor elements, then select
the last (going downwards).
I would, however, like to understand why
foreign[(_at_)lang][ancestor::*[(_at_)lang]][1][ ./@lang =
./ancestor::*[(_at_)lang][1]/@lang ] doesn't work.
I've forgotten the details of the question, but I think the culprit is the
first [1]. The predicates [(_at_)lang] and [ancestor::*[(_at_)lang]] are
harmless - if
the final predicate is true, then these predicates will also be true. But
the [1] means you only select the first <foreign> element for which these
predicates apply, which is not the case for the KH and MK expressions above.
And am I right that the difference between the KH and MK
construc- tions are that the former is looking up the
ancestor axis for the first hit, whereas the latter is
looking down the ancestor axis for the last hit? Is one
"better" than the other in any significant way?
Probably the KH construction gives a better chance that the system will stop
its search of the ancestor axis early. On the other hand, it seems inelegant
having to access the @lang attribute of each ancestor twice.
Michael Kay
http://www.saxonica.com/
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