[xsl] Avoiding boneheaded mistakes in XSLT?

Subject: [xsl] Avoiding boneheaded mistakes in XSLT?
From: David Sewell <dsewell@xxxxxxxxxxxx>
Date: Tue, 28 Dec 2010 17:35:11 -0500 (EST)
This is to some extent a general programming question, as it is possible
with any programming language to write something that is syntactically
legitimate (i.e., does not throw a compile- or run-time error) but fails
to produce expected results because of a mistake in logic or something
else. I'm sure we've all had the experience of beating our heads against
a programming failure that turns out to be the result of a very simple
(aka "boneheaded") mistake that seems obvious when found. It seems to me
that this is perhaps more likely with XSLT/XPath than some other
environments, because of (1) the general verbosity of expression, and
(2) the many complexities of return values when you're working with a
combination of XML documents and fragments, and sequences of nodes
and/or atomic values.

Over the last few days I've been working on some especially complex
transforms and have lost more time that I'd like owing to some of these
simple mistakes. Not the first time by a long shot I've made them, either. For

1. In an XPath expression, using "something/node" where I wanted
"something/node()" [ditto text vs. text()]: always means zero results and
can drive you crazy if you don't notice the missing parentheses;

2. Using xsl:copy-of instead of xsl:apply-templates in a case where
recursive processing is in fact needed on the item in question;

3. Using xsl:value-of when you really need xsl:copy-of for a variable
that is a sequence;

4. Bad logic with xsl:analyze-string, putting processing into
xsl:non-matching-substring that should have gone into
xsl:matching-substring or vice versa.

Do these sound familiar? Other favorite traps?

Has anyone come up with a useful list of "things to check any time my
code is not working the way it should"?


David Sewell, Editorial and Technical Manager
ROTUNDA, The University of Virginia Press
PO Box 400314, Charlottesville, VA 22904-4314 USA
Email: dsewell@xxxxxxxxxxxx   Tel: +1 434 924 9973
Web: http://rotunda.upress.virginia.edu/

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