what is the proper group require in comp.xml

hi,
i'd like to add a new group to comp.xml file which is just a collection
of other groups. i'd like to add something like this:
  <group>
    <id>my-x11</id>
    <name>My X11 packages</name>
    <default>false</default>
    <uservisible>true</uservisible>
    <grouplist>
      <groupreq>base-x</groupreq>
      <groupreq>gnome-desktop</groupreq>
    </grouplist>
  </group>
and i'd like to install:
yum groupinstall my-x11
but it doesn't seems to working. i like to create a new group which
include all basic x11 packages (which called on different groups on el5,
el6 and fedora*). what is the proper format to define such group?
anyway is the any docs about is somewhere? i can't find it.
thanks in advance.
regards.

-- 
  Levente                               "Si vis pacem para bellum!"