search other xml document from xsl

If I have the following xml

<root>
  <message id="foo.msg"/>
</root>

and I want to be able to lookup the message id in another xml file from with my xsl file, how do I accomplish this with XPATH?

<messages>
  <message id="foo.error" value="Hello Foo" />
  <message id="bar.msg" value="Hello Bar" />
</messages>

I'm thought that the fragment would look something like
 
  <xsl:template match="message">
    <xsl:value-of select="document('messages.xml')/message/message/@id='@id'
  </xsl:template>

What I would like to return is the "value" element.

Thanks,
Jay


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