[xsl] Flatten a sequence to a string in xslt 2.0

["Andrew Welch" <AWelch@xxxxxxxxxxxxxxx>]

With this xml:

<root>
  <node>hello</node>
  <node>world</node>
</root>

And this variable definition:

<xsl:variable name="foo" select="/root/node"/>

I get a sequence of two nodes rather than the string value of the first
node (as in xslt 1.0)

Say I want to use $foo in another function, something like:

substring-after(.,$foo)

how do I get from the sequence to a string? I hope I'm not being really
dumb here and missing something obvious :)

thanks
andrew