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Re: [xsl] Help describing the behavior of a Path Expression

2019-06-05 11:20:05
Dr Kay -
Thanks for the explanation and the link - that's helpful and clarifying.


On Tue, Jun 4, 2019 at 6:07 PM Michael Kay mike(_at_)saxonica(_dot_)com <
xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:

There are three templates here, that match overlapping sets of nodes. None
has an explicit priority, so each takes a default priority based on the
form of the match pattern. The rules are here:


The rules indicate that the priority for "node()" is -0.5 (rule 10); the
priority for "item" is 0 (rule 6), and the priority for
"item[discount[...]]" is +0.5 (rule 11). Each <item> element selected by an
xsl:apply-templates instruction is processed using the highest-priority
rule that it matches.

In this example the default rules for priorities have the desired effect.
This isn't always the case. In more complex cases, it's good practice to
allocate explicit priorities using the "priority" attribute.

Michael Kay

On 4 Jun 2019, at 21:06, Bridger Dyson-Smith bdysonsmith(_at_)gmail(_dot_)com 
xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:

Hi all -

apologies for the awkward title. I was helping a coworker with a problem,
where we wanted to ignore certain elements that didn't meet certain
requirements. We had a working template for the elements with requirements,
but how to make the processor ignore the others? My suggestion was to write
an empty template for the element (`item` below), with the paraphrased
explanation: "the processor with ignore the general expression but match on
the specific expression", but I'm clueless about the "why doesn't the
processor ignore all of the `item` elements, then?". I have the sense that
explanation might be approximately right, but it (and I) would benefit from
an improved understanding of what's actually happening.

Would someone be willing to share some better words to describe this? Is
it as easy as saying that since $expression-a (`item[discount]`) has a
predicate, it has a higher precedence than $expression-b (`item`) (or maybe
more simply: operator precedence - I see a note in Dr. Kay's XSLT/XPath 2.0
book about this)?

Thanks in advance for your time and trouble.

Here's a contrived example of our source document:
<!-- source -->
  <item color="red" size="m">
  <item color="blue" size="m">
    <discount percentage="20"/>
  <item color="yellow" size="l">
    <discount percentage="10"/>

And a stylesheet:
<!-- xsl -->
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
  <xsl:output encoding="UTF-8" method="xml" indent="yes"/>
  <xsl:strip-space elements="*"/>

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

  <xsl:template match="item[discount[@percentage ge '15']]">
    <discount-item color="{@color}" size="{@size}" price="{price}"

  <xsl:template match="item"/>
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