> 
> Implying that a function can't return any node set with 
> a document node?
>   

You can do it according to the Nov draft by

<xsl:function ..
  <xsl:variable name="tree">
    <a>tree</a>
  </xsl:variable>
  <xsl:sequence select="$tree"/>
</xsl:function>

But that's a bit cumbersome, so we've added an xsl:document element to
create document nodes explicitly:

<xsl:function ..
  <xsl:document>
    <a>tree</a>
  </xsl:document>
</xsl:function>

This will appear in the next draft.

Michael Kay