> Yes, thanks, it's becoming clearer although I'm still having issues
> with a "document" containing three root nodes that are all siblings.

that was allowed in xslt1 as well.
http://www.w3.org/TR/xslt#root-node-children
   ...In particular, it may have text node children, and any number of
     element node children. When written out using the XML output method (see
     [16 Output]), it is possible that a result tree will not be a
     well-formed XML document; however, it will always be a well-formed
     external general parsed entity. 


    When the source tree is created by parsing a well-formed XML
    document, the root node of the source tree will automatically
    satisfy the normal restrictions of having no text node children and
    exactly one element child. When the source tree is created in some
    other way, for example by using the DOM, the usual restrictions are
    relaxed for the source tree as for the result tree. 


another way that was possible in most xslt1 systems was to use 
<xsl:variable name="x">
 <foo/>
 <foo/>
 <foo/>
</xsl:variable>

select="xx:node-set($x)"

although of course the spec couldn't say that as it couldn't refer to
extensions.




David