Smart Key - Default Context

Finally, if pressed within an unrecognized context:
  ACTION KEY
     Runs the function stored in action-key-default-function.
     By default, it just displays an error message.  Set it to
     hyperbole if you want it to display the Hyperbole
     minibuffer menu or hyperbole-popup-menu to popup the
     Hyperbole menubar menu.
  ASSIST KEY
     Runs the function stored in assist-key-default-function.
     By default, it just displays an error message.  Set it to
     hkey-summarize if you want it to display a summary of
     Smart Key behavior.