Grail consists of an interface and tools for handling
gesture recognition and gesture instantiation.

When a multitouch gesture is performed on a device,
the recognizer emits one or several possible gestures.
Once the context of the gesture is known, i.e.,
in what window the touches land and what gestures
the clients of that window listen to, the instantiator
delivers the matching set of gestures.

The library handles tentative gestures, i.e.,
buffering of events for several alternative gestures
until a match is confirmed.