They're differents things.  Nodes are nodes in a tree, while items
  are just items of a sequence.  Nodes can be text(), element(), etc.


Not exactly, every value that matches node() also matches item() but
item() also includes atomic values.  In Xpath2 nodes don't have to be in
a tree, if you go

<xsl:variable name="x" as="element()">
<x/>
</xsl:variable>

then $x is an element node that does not live in a tree (it has no
parent, and no children) some Xpath functions are restricted to elements
that _do_ live in a tree (defined as meaning that root() is an instance
of document-node()) but most operations on these parentless elements
work as you would expect (so long as you expect the right thing)

David

________________________________________________________________________
This e-mail has been scanned for all viruses by Star. The
service is powered by MessageLabs. For more information on a proactive
anti-virus service working around the clock, around the globe, visit:
http://www.star.net.uk
________________________________________________________________________