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+FRAME
+
+The touch frame, consisting of a set of simultaneous contacts.
+
+CONTACT
+
+The current MT contact configuration. Changes whenever an id changes.
+
+TOUCH
+
+The current touch configuration. Changes whenever the number of contacts
+changes. A touch frame is well-defined a time T after the last
+configuration change. This allows for simultaneous touches being
+handled. It also allows for a very quick change of one finger to
+another. Such an action changes the CONTACT state, but it does not change
+the TOUCH state.
+
+DRAG/PINCH/ROTATE
+
+A transformation based on the touch frame.
+
+GESTURES
+
+Two creation points may be grouped if they are close in space-time, and
+they are always close within the same controlling entity. There can be only
+one controlling entity per point, and that decision is made upon
+creation. The window manager is a controlling entity. Ambiguities can occur
+between close points, and are resolved either by state rule or by
+priority. Relaxing the time closeness criteria has no effect within a
+controlling entity, but creates a larger set of ambiguous and undesired
+groupings, which is considered inferior.