> 
> It's a sanity question, but anyway ...
> Can I distribute product under license other than GPL if I use parts
> of documentation of some GNU tool ? i.e. if I would do readline wrapper,
> can I use parts of readline documentation for describing the functionality ?
> I think it would be okay, but I'm not quite sure.

No, see:

                  GNU GENERAL PUBLIC LICENSE
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. This License applies to any program or other work which contains
a notice placed by the copyright holder saying it may be distributed
under the terms of this General Public License.  The "Program", below,
refers to any such program or work 

....

2. You may modify your copy or copies of the Program or any portion
of it, thus forming a work based on the Program, and copy and
distribute such modifications or work under the terms of Section 1
above, provided that you also meet all of these conditions:

...
b) You must cause any work that you distribute or publish, that in
    whole or in part contains or is derived from the Program or any
    part thereof, to be licensed as a whole at no charge to all third
    parties under the terms of this License.
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

-- 
Zdenek Salvet                                              salvet@ics.muni.cz 
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           If God had meant for us to be in the Army,
         we would have been born with green, baggy skin.