> I apologize for this, but it looks like I slightly misstated the
> problem. I tested your solution and it looks like exactly what I'm
> looking for, with one difference: it is not <a> that contains the
> superset of attributes, with <b> containing a subset. It's actually
> <b> that contains the superset, and <a> contains the subset.
>
> This variation seems to work for me:
>
> <xsl:variable name="file2" select="document('2.xml')/outsidedata"/>
> <xsl:template match="a">
>   <xsl:variable name="a" select="." />
>   <xsl:for-each select="$file2/b[@* = $a/@*]">
>     <xsl:variable name="b" select="." />
>     <xsl:variable name="test">
>       <xsl:for-each select="$a/@*">
>         <xsl:if test="not($b/@*[name() = name(current())] = .)">
>           no attribute with the same name on element b whose value 
equals this one
>         </xsl:if>
>       </xsl:for-each>
>     </xsl:variable>
>     <xsl:if test="not(string($test))">
>       [<xsl:value-of select="."/>]
>     </xsl:if>
>   </xsl:for-each>
> </xsl:template>
Hi Zack,
I don't understand why Jeni's solution should be wrong. With your sentence
<p>The quick brown <a x="1" y="2" z="3">fox</a> jumps over the lazy <a 
x="9" y="8" z="7">dog</a>.</p>
and the second file
<outsidedata>
  <b x="1" y="2">PPP</b>
  <b y="2" z="3">QQQ</b>
  <b z="3">RRR</b>
  <b x="9" z="7">SSS</b>
  <b m="2" z="3">TTT</b>
</outsidedata>
I get the output
"The quick brown [PPP][QQQ][RRR] jumps over the lazy [SSS]."
This is exactly what I expect after reading your first posting again. 
With your stylesheet I get
"The quick brown jumps over the lazy ."
This seems not to be ok. I thought that the <b>s must not have all 
attributes from <a>, but may not have other than <a> and not the same 
with a different value.
And my comments/questions to Jeni's stylesheet:
>><xsl:template match="a">
>>  <xsl:variable name="a" select="." />
 <xsl:for-each select="$file2/b[@* = $a/@*]">
I thought of a filter too, but I didn't find a sensible one. The above 
one isn't completely logical to me. What exactly does it mean? Maybe 
"all <b>s, whose all attributes are in <a> and don't have a different 
value"?
   <xsl:variable name="test">
     <xsl:for-each select="@*">
       <xsl:if test="not($a/@*[name() = name(current())] = .)">
This is a little bit easier ;-)
         no attribute with the same name on element a whose value
         equals this one
       </xsl:if>
     </xsl:for-each>
   </xsl:variable>
   <xsl:if test="not(string($test))">
This is easier again. Of course a test on "contains($test, 'false')" is 
not necessary.
     <xsl:text />[<xsl:value-of select="." />]<xsl:text />
   </xsl:if>
 </xsl:for-each>
</xsl:template>
Joerg
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