Just for fun I've created exslt2.xslt and exslt2-test.xslt to model concepts discussed at EXSLT 2.0 forum. I did nothing special but used tuple as reference, and also I've defined f:call() to make function call indirectly.

<?xml version="1.0" encoding="utf-8"?>
<!--
  exslt 2 sketches.
-->
<xsl:stylesheet version="2.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:f="http://exslt.org/v2"
  xmlns:t="this"
  xmlns:p="private"
  exclude-result-prefixes="xs t f">

  <xsl:include href="exslt2.xslt"/>

  <xsl:template match="/" name="main">
    <root>
      <xsl:variable name="refs" as="item()*" select="
        for $i in 1 to 20 return
          f:ref(1 to $i)"/>

      <total-items>
        <xsl:sequence select="
          sum
          (
            for $ref in $refs return
              count(f:deref($ref))
          )"/>
      </total-items>

      <sums-per-ref>
        <xsl:for-each select="$refs">
          <xsl:variable name="index" as="xs:integer" select="position()"/>

          <sum
            index="{$index}"
            value="{sum(f:deref(.))}"/>
        </xsl:for-each>
      </sums-per-ref>

      <add>
        <xsl:text>1 + 2 = </xsl:text>
        <xsl:sequence select="f:call(xs:QName('t:add'), (1, 2))"/>
      </add>
      </root>
  </xsl:template>

  <xsl:function name="t:add" as="xs:integer">
    <xsl:param name="arguments" as="xs:integer+"/>

    <xsl:variable name="first" as="xs:integer" select="$arguments[1]"/>
    <xsl:variable name="second" as="xs:integer" select="$arguments[2]"/>

    <xsl:sequence select="$first + $second"/>
  </xsl:function>

</xsl:stylesheet>

Code can be found at saxon.extensions.9.1.zip.