design question on function namespaces

  <xsl:function name="mods:year">
    <xsl:param name="bibref" as="element(mods:mods)"/>
    <xsl:for-each select="$bibref">
      <xsl:value-of  select="substring((mods:originInfo/mods:dateIssued,
			mods:relatedItem/mods:originInfo/mods:dateIssued,
			mods:relatedItem/mods:part/mods:date)[1],1,4)" />
    </xsl:for-each>
  </xsl:function>

declare function display:year($rec as element()) as xs:string? {
       substring(($rec/mods:originInfo/mods:dateIssued,
       $rec/mods:relatedItem/mods:originInfo/mods:dateIssued,
       $rec/mods:relatedItem/mods:part/mods:date)[1],1,4)
};