xslt key used with a predicate of an xpath expression

Hello,

Lines 20-22 of the following xsl script do not work as I'd hoped.
A way to get what I'd hoped is on lines 25-28.

Is the key used in 20-22 passed directly to 'xpath' before being
evaluated by 'xslt'?
Is there a way to accomplish this without creating an extra variable
as in the solution on 25-28?

I think it is too hard to explain the problem in English, so please
excuse my terse canonical description. If you would like more of a
description, please ask.

Regards,
Tim Lebo


======== XML input =========
<?xml version="1.0" encoding="UTF-8"?>
<root>
  <object id="obj1" colorhex="#ffffff">
  </object>
  <object id="obj2" colorhex="#000000">
  </object>
  <object id="obj3" colorhex="#ffffff">
  </object>
  <thing>
          <idref>obj1</idref>
        </thing>
</root>


 ======== XSLT attempt ========
   1 <?xml version="1.0"?>
      2 <xsl:transform
xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
      3 <xsl:output method="text"/>
      4
      5 <xsl:variable name="colors">
      6   <color hex="#ffffff">White</color>
      7   <color hex="#000000">Black</color>
      8 </xsl:variable>
      9
     10 <xsl:key name="objects" match="object" use="@id"/>
     11
     12 <xsl:template match="/">
     13   <xsl:apply-templates select="root/thing"/>
     14 </xsl:template>
     15
     16 <xsl:template match="thing">
     17   <xsl:value-of select="concat('This thing refers to object
with @id ',idref,$NL)"/>
     18   <xsl:value-of select="concat('The object with that id has
@colorhex = ',
     19
key('objects',idref)/@colorhex,$NL)"/>
     20   <xsl:value-of select="concat('The @hex of that object means
color ',
     21
$colors/color[@hex=key('objects',idref)/@hex],
     22                                 ' (THIS DOES NOT WORK BUT I
WANT IT TO.)',$NL)"/>
     23
     24   <xsl:comment> The following accomplishes the desired output
</xsl:comment>
     25   <xsl:variable name="tempvar"
select="key('objects',idref)/@colorhex"/>
     26   <xsl:value-of select="concat('Value of undesireable variable
is ',$tempvar,$NL)"/>
     27   <xsl:value-of select="concat('The round-about way to get the
color meaning is ',
     28                                 $colors/color[@hex=$tempvar],$NL)"/>
     29 </xsl:template>
     30
     31 <xsl:variable name="NL">
     32 <xsl:text>
     33 </xsl:text>
     34 </xsl:variable>
     35
     36 </xsl:transform>



======= XSLT without line numbers so you can run it yourself ======
<?xml version="1.0"?>
<xsl:transform xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="2.0">
<xsl:output method="text"/>

<xsl:variable name="colors">
  <color hex="#ffffff">White</color>
  <color hex="#000000">Black</color>
</xsl:variable>

<xsl:key name="objects" match="object" use="@id"/>

<xsl:template match="/">
  <xsl:apply-templates select="root/thing"/>
</xsl:template>

<xsl:template match="thing">
  <xsl:value-of select="concat('This thing refers to object with @id
',idref,$NL)"/>
  <xsl:value-of select="concat('The object with that id has @colorhex = ',
                                key('objects',idref)/@colorhex,$NL)"/>
 <xsl:value-of select="concat('The @hex of that object means color ',

$colors/color[@hex=key('objects',idref)/@hex],
                                ' (THIS DOES NOT WORK BUT I WANT IT
TO.)',$NL)"/>

  <xsl:comment> The following accomplishes the desired output </xsl:comment>
  <xsl:variable name="tempvar" select="key('objects',idref)/@colorhex"/>
  <xsl:value-of select="concat('Value of undesireable variable is
',$tempvar,$NL)"/>
  <xsl:value-of select="concat('The round-about way to get the color
meaning is ',
                                $colors/color[@hex=$tempvar],$NL)"/>
</xsl:template>

<xsl:variable name="NL">
<xsl:text>
</xsl:text>
</xsl:variable>

</xsl:transform>