Like imageclass, applications do not normally create objects of
gadgetclass, but instead create objects of its subclasses. currently,
gadgetclass has four subclasses:

propgclass
    An easy to implement, horizontal or vertical proportional gadget.

strgclass
    A string gadget.

groupgclass
    A special gadget class that creates one composite gadget out of
    several others.

buttongclass
    A button gadget that keeps sending button presses while the user
    holds it down.

buttongclass has a subclass of its own:

frbuttonclass
    A buttongclass gadget that outlines its imagery with a frame.

For specific information on these classes, see the Boopsi Class Reference
in the appendix b of this manual.