Document touch event

docs/GestureResponderSystem.md

@@ -39,11 +39,24 @@ If the View returns true and attempts to become the responder, one of the follow
 
 If the view is responding, the following handlers can be called:
 
- - `View.props.onResponderMove: (moveEvt) => {}` - The user is moving their finger
- - `View.props.onResponderRelease: (releaseEvt) => {}` - Fired at the end of the touch, ie "touchUp"
+ - `View.props.onResponderMove: (evt) => {}` - The user is moving their finger
+ - `View.props.onResponderRelease: (evt) => {}` - Fired at the end of the touch, ie "touchUp"
  - `View.props.onResponderTerminationRequest: (evt) => true` - Something else wants to become responder. Should this view release the responder? Returning true allows release
  - `View.props.onResponderTerminate: (evt) => {}` - The responder has been taken from the View. Might be taken by other views after a call to `onResponderTerminationRequest`, or might be taken by the OS without asking (happens with control center/ notification center on iOS)
 
+`evt` is a synthetic touch event with the following form:
+
+ - `nativeEvent`
+     + `changedTouches` - Array of all touch events that have changed since the last event
+     + `identifier` - The ID of the touch
+     + `locationX` - The X position of the touch, relative to the element
+     + `locationY` - The Y position of the touch, relative to the element
+     + `pageX` - The X position of the touch, relative to the screen
+     + `pageY` - The Y position of the touch, relative to the screen
+     + `target` - The node id of the element receiving the touch event
+     + `timestamp` - A time identifier for the touch, useful for velocity calculation
+     + `touches` - Array of all current touches on the screen
+
 ### Capture ShouldSet Handlers
 
 `onStartShouldSetResponder` and `onMoveShouldSetResponder` are called with a bubbling pattern, where the deepest node is called first. That means that the deepest component will become responder when multiple Views return true for `*ShouldSetResponder` handlers. This is desirable in most cases, because it makes sure all controls and buttons are usable.