[xsl] functions and sequences

[Bruce D'Arcus <bdarcus@xxxxxxxxxxxxx>]

I've run across this issue in a different context, but can't figure out 
how to apply it here.

I have this function (within a large stylesheet).  It works if I 
comment out the two lines indicated with the comments, but I get a "E 
net.sf.saxon.xpath.DynamicError: A sequence of more than one item is 
not allowed as the result of function bib:reftype()" error otherwise.  
Is there some way to get this to work?  I'm not really sure how much of 
the related code I need to show to have this make any sense!

  <xsl:function name="bib:reftype" as="xs:string">
    <xsl:param name="bibref" as="element(mods:mods)?"/>
    <xsl:choose>
      <xsl:when test="$bibref/mods:relatedItem/@type = 'host'">
        <xsl:variable name="issuance" 
select="$bibref/mods:relatedItem/mods:originInfo/mods:issuance"/>
        <xsl:choose>
          <xsl:when test="bib:refclass($bibref) = 'part-inSerial'">
            <xsl:text>article</xsl:text>
            <!-- this code introduces a sequence error; don't know why 
-->
            <xsl:text>-</xsl:text>
            <xsl:value-of select="$bibref/mods:relatedItem/mods:genre"/>
          </xsl:when>
          <xsl:when test="bib:refclass($bibref) = 'part-inMonograph'">
            <xsl:choose>
              <xsl:when test="$bibref/mods:genre">
                <xsl:value-of select="$bibref/mods:genre"/>
              </xsl:when>
              <xsl:otherwise>
                <xsl:text>chapter</xsl:text>
              </xsl:otherwise>
            </xsl:choose>
          </xsl:when>
          <xsl:otherwise>
            <xsl:value-of select="$bibref/mods:genre"/>
          </xsl:otherwise>
        </xsl:choose>
      </xsl:when>
      <xsl:otherwise>book</xsl:otherwise>
    </xsl:choose>
  </xsl:function>