[xsl] doc() concat expression and whitespace error

[Bruce D'Arcus <bdarcus@xxxxxxxxxxxxx>]

I'm working on pulling in -- using the doc() function -- documents from  
the eXist XML DB via it's http interface.

Here's my template:

  <xsl:template match="db:bibliography" mode="create-bibcollection">
    <bibliography>
      <modsCollection xmlns="http://www.loc.gov/mods/v3";>
        <xsl:for-each select="distinct-values(key('citekey', 'all'))">
  <!--+ ================================================
    | bibrecord variable identifies where to locate the bib records; in
    | this case, we access them via http from an eXist XML DB
    +-->
	  <xsl:variable name="bibrecord"
	     
select='doc(concat("http://localhost:8080/exist/servlet/db/mods? 
_query=", "/mods:modsCollection/mods:mods[@ID='", ., "']"))'/>
          <xsl:copy-of select="$bibrecord" />
        </xsl:for-each>
      </modsCollection>
    </bibliography>
  </xsl:template>

However, when I run it from Saxon, I get this error:

	  Error reported by XML parser: Whitespace required before attributes.

So, I decided to try to access a document via a web browser.  I got an  
error until I added the namespace declaration in the query.  So, this  
works from the browser:

http://localhost:8080/exist/servlet/db/biblio? 
_query=declare%20namespace%20mods=%22http://www.loc.gov/mods/v3%22;/ 
mods:modsCollection/mods:mods[@ID='Tilly2000a']

.... but this does not from Saxon:

<xsl:variable name="bibrecord"
	  
select='doc(concat("http://localhost:8080/exist/servlet/db/biblio? 
_query=declare%20namespace%20mods=%22http://www.loc.gov/mods/v3%22;";,  
"/mods:modsCollection/mods:mods[@ID='", ., "']"))'/>

I know in theory it should work, since I got the suggestion from the  
author of eXist; am just not sure where the problem is.  Is there  
something wrong with my variable select expression (which is what the  
error is being reported about) from the XSLT/Saxon side?

Bruce