|--------------------------------------|
||----------------||------------------||
||       A        ||         B        ||
||----------------||------------------||
||----------------||------------------||
||       C        ||         D        ||
||----------------||------------------||
|                . . .                 |
|--------------------------------------|

##</code><code>##

A->pack(-side=>'left');
B->pack(-side=>'right');
C->pack(-side=>'left');
D->pack(-side=>'right');