not simple (or simple? :-) xpath matching

i'm again with xsl, don't offence, but i still not convinced
about such solution. isn't it only a fancy thing? more modern,
then useful? ;-) don't answer it, i didn't ask :-) -- i'm only a
bit frustrated with following example:

<document>
   <part id="a">
      <chapter id="1"/>
      <chapter id="2"/>
      <chapter id="3"/>
   </part>
   <part id="b">
      <chapter id="1"/>
      <chapter id="2"/>
      <chapter id="3"/>
   </part>
   <part id="c">
      <chapter id="1"/>
      <chapter id="2"/>
      <chapter id="3"/>
      <chapter id="10"/>
   </part>
</document>

and now i would like to show a chapter depends on parameters in a
url eg. '?part=c&chapter=4', but also to give the closest one, if
given is not applicable (to give part=c, chapter=3 in this
example, or to give part=c, chapter=10 if asked was chapter=12)
with simple information, that is not exact match. i also need to
provide default values if parameters are empty (for now i have
<xsl:choose> construction).

i'm using cocoon1, so if it's better tu use xsp -- just say it,
but i'm very interested how to manage with both using xsl only.

-- 
Daniel `bonkey' Bauke; http://www.oho.pl/~bonkey/; {happiness=bike&&unix;}

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