thank you very much for that information. Now I use the xsl:namespace instruction to add the necessary namespace node. Unfortunately namespace nodes can not be added to document nodes. Therefore I had to introduce a wrapper element.

  <xsl:variable name="builtInListTypes">
      <xsl:namespace name="xs" select="''"/>
      <listType name="xs:IDREFS"   itemType="xs:IDREF"/>
      <listType name="xs:NMTOKENS" itemType="xs:NMTOKEN"/>
      <listType name="xs:ENTITIES" itemType="xs:ENTITY"/>

 Well, you could add the namespace to each of the listType elements, but then you would need to call xsl:namespace three times.
Michael Kay