Re: apply-templates select and current() question

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Subject: Re: apply-templates select and current() question
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Thu, 19 May 2005 15:48:50 -0400

At 02:43 PM 5/19/2005, you wrote:

I've correct the expression to self::db:footnote. For some reason that's never seemed intuitive to me (obviously).

Yes, it's a little bizarre until you get used to it.

The trick is to remember (1) that = or equality does *not* test for node type or node identity (2) node type is easily enough tested with node tests like "*" or "node()" or "name" as long as you know the axis you want to look at. ("Node test" is a formal technical term in XPath; learning what a node test is can be very helpful.) Since XPath will default to the child:: axis if your axis is not named, that means you have to do the extra work of checking on the self:: axis if you want to traverse to the node itself.

Since a node-set, coerced to a Boolean, is false for an empty set and true for a set with any nodes in it, test="self::element" will test true if the context node is an "element" element (since starting from an "element" element there is indeed an "element" element on the self:: axis).

So, it all hangs together ... but it takes practice, since a number of non-obvious design features of XPath combine to get the behavior. Note that while these come to seem normal enough once you're comfortable with the way XPath location paths are put together, they can also combine to result in more weirdness. (Languages seem to be like that: no matter what the design there are always edge cases.)

For example, self::* will return true for elements, but false when the context node is an attribute, comment, processing instruction, text node or the root (because of the way "*" is defined).

Cheers,
Wendell


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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
Mulberry Technologies, Inc.                http://www.mulberrytech.com
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Current Thread
apply-templates select and current() question Bruce D'Arcus - 19 May 2005 02:42:16 -0000 Wendell Piez - 19 May 2005 16:25:40 -0000 Bruce D'Arcus - 19 May 2005 18:43:18 -0000 Wendell Piez - 19 May 2005 19:59:59 -0000 <= <Possible follow-ups> Jarno.Elovirta - 19 May 2005 05:49:59 -0000

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