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All the Perl that's Practical to Extract and Report

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  • You’re defining two identity copies, one on the root element and one for everything else; why? Next, you write a template for //* which is equivalent to matching * (but I haven’t slept and it’s 6AM, so I might be making a mistake). And finally, you say making the D nodes sort together with all the others would be a lot of work, when actually it’s less work than you’re already doing. Overall:



    <xsl:template match="@*|node()">
        <xsl:apply-templates select="@*|node()"/>

    <xsl:template match="*">

        <xsl:apply-templates select="@*"/>

        <xsl:apply-templates select="*">
          <xsl:sort select="name()"/>
          <xsl:sort select="
              | self::D/@FOO



    I think. Untested. You may have to write things a bit differently (to groggy to recall all the details precisely), but that’s the approach.

    • Thanks. Tested and it works. I bow to your superior XSLT-fu (mine needs a lot of work). My only consolation is that I've seen worse code than mine from someone else who was trying to do the same sort of thing (and who wasn't even yet trying to sort by name()). I still find XSLT non-intuitive, e.g., how does it decide which templates to match, does it matter what in what order the templates come, and so why doesn't the first (identity) template above just match and copy everything unchanged?
      • Don’t worry, you’re in good company. Almost no one groks XSLT properly. (This is probably because every single XSLT tutorial is terrible junk.) Most of the transforms I see are seriously suboptimal, and a very large fraction of them are really atrocious. There’s a lot of cargo cult and programming by coincide in the XSLT world. Your attempt was quite decent by those standards. :-)

        Actually, the way XSLT processing happens is very simple, but because of the implicit default templates, it

        • Ugh, even a multitude of previewings did not protect me from submitting the comment with a whole bunch of small grammatical and spelling mistakes. “It’s value?” Argh. My face is melting off. I’m not stupid – I swear!

    • Huh, the order of templates is not supposed to matter, but if I switch the order of the templates above, then it doesn't work anymore. If you change the "*" template to "//*", then it works again. Which probably explains why I had "//*" in my first template. Code:


      use strict;
      use warnings;

      use XML::LibXML;
      use XML::LibXSLT;

      my $parser = XML::LibXML->new();
      my $xslt = XML::LibXSLT->new();

      my $source = $parser->parse_string(<<'EOT');
      <?xml version="1.0" encoding="UTF-8"?>

      • Aha...from the docs []:

        It is an error if this leaves more than one match. An XSLT processor may signal the error; if it does not signal the error, it must recover by choosing, from amongst the matches that are left, the one that occurs last in the stylesheet.
        • So it would probably be better to put an explicit priority on the "*" template.
          • Or use something more restrictive than node() in the identity transform to avoid matching elements, eliminating the conflict in the first place. The types a node can have are element, text, comment and processing instruction. Matching any node except elements therefore translates to XPath as “text()|comment()|processing-instruction()”. Another, possibly better way to write that (certainly a shorter one) is “node()[not(self::*)]”. (The predicate “[]” constrains the node()