Originally the main menu was a center of operations from which a variety of initial conditions for a fixed rule could be set up and their evolution watched. Alternatively, one of a number of demonstrations could be chosen and set in motion. This is still a significant style of operation, but the number of rule configurations has grown, often bringing with them a specialized submenu of their own.
This increase in versatility has given fundamental importance to the options r and l, which permit editing the rules, or editing the bitplanes, respectively. In turn, this has created a tendency to repeat many of the operations of the main menu over again within each of the submenus. The increase in the total length of CAMEX is more than compensated by the increase in user convenience.
The particular rule, or the particular viewpoint toward the planes, is established via one of the other menus, typically the one accessible under f1; Conway's Life is the default choice, as it is always an interesting automaton to work with.