Re: [xsl] Using node-set variables in predicates (another node comparison question)

["Eliot Kimber eliot.kimber@xxxxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Note that this function:

<xsl:function name="mine:is-trim-element" as="xs:boolean">
    <xsl:param name="elt" as="node()"/>
    <xsl:value-of select="exists($elt[self::desc or self::dt or self::endnote
or self::entry or self::example-title or self::glossterm or self::li or
self::msg-severity or self::p or self::shortdesc or self::title or
self::value-allowed or self::value-default or self::value-type])"/>
  </xsl:function>

Should use xsl:sequence instead of value-of as you want to return a Boolean
value.

By using value-of you are effectively constructing a Boolean (result of
exists()) then converting that to a text node (result of value-of) and then
XSLT implicitly converts that back to a Boolean using the string value of the
text node.

In general, you almost always want xsl:sequence unless what you really want is
a text node (for example, because youre contributing to the content of a
result element).

[Wendell beat me to this suggestion but Id already written it:]

As for the question of determining the type: I think I would follow Dimitres
advice and use templates :

<xsl:function name=mine:is-trim-element as=xs:boolean>
    <xsl:param name="elt" as="node()"/>
  <xsl:apply-templates select=$elt mode= mine:is-trim-element/>
</xsl:function>

<xsl:template mode= mine:is-trim-element as=xs:Boolean
  match=desc | endnote | dt
 >
  <xsl:sequence select=true()/>
</xsl:template>

<xsl:template mode= mine:is-trim-element as=xs:Boolean priority=-1
match=*>
  <xsl:sequence select=false()
</xsl:template>

This makes the logic for determining type extensible using normal extension
mechanisms.

Cheers,

E.

_____________________________________________
Eliot Kimber
Sr Staff Content Engineer
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From: Chris Papademetrious christopher.papademetrious@xxxxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Tuesday, January 4, 2022 at 2:37 PM
To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx <xsl-list@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [xsl] Using node-set variables in predicates (another node
comparison question)
[External Email]

Hi Dimitre,

That is good advice about functions  I will keep it in mind!


Hi everyone,

So I ran into a limitation of using document node-set variables in template
match expressions:

  <!-- put document nodes in $trim-elements -->
  <xsl:variable name="trim-elements"
select="//(desc|dt|entry|glossterm|li|p|shortdesc|title)"/>

  <!-- reference elements in $trim-elements -->
  <xsl:template match="text()
                       [matches(., '^\s+')]
                       [ancestor::*[. intersect
$trim-elements][not(descendant::*[. intersect $trim-elements])]]
                       [not(ancestor-or-self::node()
                         [ancestor::*[. intersect
$trim-elements][not(descendant::*[. intersect $trim-elements])]]
                         [preceding-sibling::node()])]">

When I constructed a temporary <p> node in a variable:

xsl:variable name="temporary-p">
   <p><xsl:copy-of select=blah blah></p>
</xsl:variable>

then called <xsl:apply-templates> to apply the template:

<xsl:apply-templates select="$temporary-p"/>

the template did not get applied. This makes perfect sense  my temporary <p>
variable does not contain any document nodes at all, so the template match
expression would never match!

But with Dimitres advice about functions fresh in my mind, I converted my
document-node variable into a node-type function:

  <xsl:function name="mine:is-trim-element" as="xs:boolean">
    <xsl:param name="elt" as="node()"/>
    <xsl:value-of select="exists($elt[self::desc or self::dt or self::endnote
or self::entry or self::example-title or self::glossterm or self::li or
self::msg-severity or self::p or self::shortdesc or self::title or
self::value-allowed or self::value-default or self::value-type])"/>
  </xsl:function>

Now I can use the function instead of the variable in the match expression:

  <xsl:template match="text()
                       [matches(., '^\s+')]
                       [ancestor::*[mine:is-trim-element(.)][not(descendant::
*[mine:is-trim-element(.)])]]
                       [not(ancestor-or-self::node()
                         [ancestor::*[mine:is-trim-element(.)][not(descendant
::*[mine:is-trim-element(.)])]]
                         [preceding-sibling::node()[not(mine:is-invisible(.))
]])]">

and the template applies as expected to my temporary variable!

Follow-up question  is there some syntactic sugar that would allow me to
write

self::(a|b|c)

instead of

(self::a or self::b or self::c)

or some other way of testing the element type in $elt altogether? I have
another function that matches several dozen element types, and a more compact
representation would be nice. I thought about matching local-name() against a
list of tag names using intersect, but that is not much shorter and it seems
operationally clunkier.

Thanks, this has been an enjoyable exercise for learning!


  *   Chris


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