Often, users find it convenient to control gadgets using the keyboard.
Starting with V37, it is possible to denote the keyboard equivalent for a
GadTools gadget.  The keyboard equivalent will be an underscored character
in the gadget label, for easy identification.  At the present time,
however, the application is still responsible for implementing the
reaction to each keypress.

 denoting a gadget's keyboard equivalent 
 implementing a gadget's keyboard equivalent behavior