XSLT compatibility problem between XLAN and SAXON

When I'm implementing an XSLT to transform IRIS data dictionary items value (numbers, e.g. 02 08 etc) to descriptive texts for preview page, I found an incompatibility problem between XLAN and SAXON XSLT processor. It's mainly caused by the usage of tokenize funciton. The solution I found is:

<xsl:stylesheet version="1.0" 
                  xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
                  xmlns:iris="http://iris-database.org/iris"
                  xmlns:str="http://exslt.org/strings"
                  exclude-result-prefixes="xsl str">

......

      <xsl:choose>

        <!-- For XLAN -->
        <xsl:when test="function-available('str:tokenize')">
          <xsl:for-each select="str:tokenize(.,' ')">
            <xsl:variable name="currentType" select="."/>
            <xsl:if test=".!='999'">
              <iris:instrumentType><xsl:value-of select="$ddDoc/IRIS_Data_Dict/instrument/typeOfInstruments//type/@label[../@value=$currentType]"/></iris:instrumentType>
            </xsl:if>
            <xsl:if test=".='999'">
              <iris:instrumentType><xsl:value-of select="$newType"/></iris:instrumentType>
            </xsl:if>
          </xsl:for-each>
        </xsl:when>

        <!-- For SAXON -->
        <xsl:otherwise>  
          <xsl:for-each select="tokenize(.,' ')">
            <xsl:variable name="currentType" select="."/>
            <xsl:if test=".!='999'">
              <iris:instrumentType><xsl:value-of select="$ddDoc/IRIS_Data_Dict/instrument/typeOfInstruments//type/@label[../@value=$currentType]"/></iris:instrumentType>
            </xsl:if>
            <xsl:if test=".='999'">
              <iris:instrumentType><xsl:value-of select="$newType"/></iris:instrumentType>
            </xsl:if>
          </xsl:for-each>
        </xsl:otherwise>
      </xsl:choose>