Re: [xsl] xsl:fallback, nodesets, and different processors

[Jeni Tennison <mail@xxxxxxxxxxxxxxxx>]

Hi Matthew,

> I am a bit confused by the <xsl:fallback> element. Perhaps someone
> can help me out with a strategy for the following problem. To make
> things easier, I have simplified my XSL below.
>
> I want to modify my template to use the built-in XSLT 1.0 nodeset
> support but also still support the older xalan processor that uses
> the xalan:nodeset extension for the same thing.

(You mean the built-in XSLT 1.1 RTF-to-nodeset conversion, not XSLT
1.0.)

The xsl:fallback element is for use with new or extension *elements*.
If you nest xsl:fallback within a new or extension element, then a
processor will use the content of the xsl:fallback if it doesn't
recognise the element. For example, if you wanted to use the XSLT 1.1
xsl:document element, or fall back on the redirect:write element, then
you could do:

  <xsl:document href="...">
    ...
    <xsl:fallback>
      <redirect:write file="...">
        ...
      </redirect:write>
    </xsl:fallback>
  </xsl:document>

What you want to do, however, is test whether the processor supports
XSLT 1.1. You can do that by testing the system property
'xsl:version', as follows:

<xsl:template match="table">
  <xsl:choose>
    <xsl:when test="system-property('xsl:version') >= 1.1">
      <xsl:for-each select="$cellFilter/table/cell">
        ...
      </xsl:for-each>
    </xsl:when>
    <xsl:otherwise>
      <xsl:for-each select="xalan:nodeset($cellFilter)/table/cell">
        ...
      </xsl:for-each>
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>

I would also recommend that you use the function-available() function
to test whether xalan:nodeset() is available before you use it:

<xsl:template match="table">
  <xsl:choose>
    <xsl:when test="system-property('xsl:version') >= 1.1">
      <xsl:for-each select="$cellFilter/table/cell">
        ...
      </xsl:for-each>
    </xsl:when>
    <xsl:when test="function-available('xalan:nodeset')">
      <xsl:for-each select="xalan:nodeset($cellFilter)/table/cell">
        ...
      </xsl:for-each>
    </xsl:when>
    <xsl:otherwise>
      <xsl:message terminate="yes">
        This stylesheet requires a processor that implements XSLT 1.1
        or Xalan.
      </xsl:message>
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>

I hope that helps,

Jeni

---
Jeni Tennison
http://www.jenitennison.com/


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