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Re: [xsl] Ignoring ambiguous matches


Subject: Re: [xsl] Ignoring ambiguous matches
From: Ihe Onwuka <ihe.onwuka@xxxxxxxxx>
Date: Thu, 13 Feb 2014 01:40:59 +0000

Give or take the priority setting it would look something like a
series of templates of the following ilk.

  <xsl:template match="@title" priority="99">
    <xsl:param name="title" select="."/>
    <xsl:next-match>
      <xsl:with-param name="title" select="replace($title, 'some regex','')"/>
    </xsl:next-match>
  </xsl:template>

The alternative is a humongous regex or the introduction of
intermediate variables ($title1, $title2 etc....) to allow you to
break the humongous regex down. This is what I started with and will
probably revert to as the next-match way introduces alot of
boiler-plate and I can't afford the distraction of figuring out
whether and how to abstract it away.




On Thu, Feb 13, 2014 at 1:35 AM, Graydon <graydon@xxxxxxxxx> wrote:
> On Thu, Feb 13, 2014 at 01:06:25AM +0000, Ihe Onwuka scripsit:
>> I am about to write several template rules that will all match the
>> same node but will each apply (or try to apply) a different edit.
>>
>> I don't care the order in which these are applied as long as each gets
>> a shot at applying it's edit.
>>
>> I was wondering whether I can just ignore the ambiguous match warnings
>> and be confident that everything is A - ok or whether I have to
>> diligently invent template priorities to prevent that.
>
> If you need everything to match, it's not safe to ignore ambiguous rule
> match warnings; you're going to get only one of the rules matching,
> hopefully the last one.
>
> For XSLT 2.0, last thing in section 6.4 of the spec:
>
> "It is a recoverable dynamic error if the conflict resolution algorithm
> for template rules leaves more than one matching template rule. The
> optional recovery action is to select, from the matching template rules
> that are left, the one that occurs last in declaration order."
>
> Why not find the node and do everything you need to do to that node
> inside that template.
>
> Usually something like
>
> <xsl:variable name="pass1">
>     <xsl:apply-templates mode="pass1" select="."/>
> </xsl:variable>
>
> <xsl:variable name="pass2">
>     <xsl:apply-templates mode="pass2" select="$pass1"/>
> </xsl:variable>
>
> and eventually
>
> <xsl:sequence select="$passn"/>
>
> Whatever transform you want at each step has to be present as templates
> with the appropriate modes.
>
> Next match for multiple templates is tricky, you have to be sure all the
> templates have exactly the same priority or set the priorities carefully
> and this, well, there's a reason one generally prefers to let the
> processor deal with priority.
>
> -- Graydon


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