Using condition expression with an empty string variab

Hi,

I have applied the following condition expression successfully to my job.
And this expression pattern is suggested by Jeni back in May xsl
list.(msg00890.htm)

   [@FacilityID[string($office)]=$office]

  which   is supposed to handle situations as:
  when variable **office** is a given string,  then the condition will be
applied.
  when variable **office** is an empty string, then the condition will not
be used.

  Now I try to apply the expression to a simple case like example below,
  it does not function correctly for the given empty string,  it produces a
  set of empty nodes instead.   Why?

Would  anyone provide some suggestions?


  ** xml  **
<?xml-stylesheet href="test.xsl" type="text/xsl"?>
<docs>
<z-row FacilityID="xxx" ProductID="aaa"/>
<z-row FacilityID="yyy" ProductID="bbb"/>
<z-row FacilityID="zzz" ProductID="ccc"/>
</docs>

**  xsl ***
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes"/>

<xsl:template match="/">
<xsl:variable name="office" select="''"/> <!-- input an empty string -->
<xsl:variable name="xx"
select="//z-row[@FacilityID[string($office)]=$office]"/>
<xsl:copy-of select="$xx"/>
</xsl:template>
</xsl:stylesheet>


  Thanks.

  Sun-fu Yang,

  sfyang@xxxxxxxxxxxxx




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