Add Hover,Focus,Press docs to REAMDE (#15328)

Author: necolas

packages/react-events/README.md

@@ -1,3 +1,143 @@
 # `react-events`
 
-This is package is intended for use with the experimental React events API.
+*This package is experimental. It is intended for use with the experimental React
+events API that is not available in open source builds.*
+
+
+## Focus
+
+The `Focus` module responds to focus and blur events on the element it wraps.
+Focus events are dispatched for `mouse`, `pen`, `touch`, and `keyboard`
+pointer types.
+
+```
+type FocusEvent = {}
+```
+
+### disabled: boolean
+
+Disables all `Focus` events.
+
+### onBlur: (e: FocusEvent) => void
+
+Called when the element loses focus.
+
+### onFocus: (e: FocusEvent) => void
+
+Called when the element gains focus.
+
+### onFocusChange: boolean => void
+
+Called when the element changes hover state (i.e., after `onBlur` and
+`onFocus`).
+
+
+## Hover
+
+The `Hover` module responds to hover events on the element it wraps. Hover
+events are only dispatched for `mouse` pointer types. Hover begins when the
+pointer enters the element's bounds and ends when the pointer leaves.
+
+```
+type HoverEvent = {}
+```
+
+### disabled: boolean
+
+Disables all `Hover` events.
+
+### onHoverStart: (e: HoverEvent) => void
+
+Called once the element is hovered. It will not be called if the pointer leaves
+the element before the `delayHoverStart` threshold is exceeded. And it will not
+be called more than once before `onHoverEnd` is called.
+
+### onHoverEnd: (e: HoverEvent) => void
+
+Called once the element is no longer hovered. It will be cancelled if the
+pointer leaves the element before the `delayHoverStart` threshold is exceeded.
+
+### onHoverChange: boolean => void
+
+Called when the element changes hover state (i.e., after `onHoverStart` and
+`onHoverEnd`).
+
+### delayHoverStart: number
+
+The duration of the delay between when hover starts and when `onHoverStart` is
+called.
+
+### delayHoverEnd: number
+
+The duration of the delay between when hover ends and when `onHoverEnd` is
+called.
+
+
+## Press
+
+The `Press` module responds to press events on the element it wraps. Press
+events are dispatched for `mouse`, `pen`, `touch`, and `keyboard` pointer types.
+
+```
+type PressEvent = {}
+```
+
+### disabled: boolean
+
+Disables all `Press` events.
+
+### onPressStart: (e: PressEvent) => void
+
+Called once the element is pressed down. If the press is released before the
+`delayPressStart` threshold is exceeded then the delay is cut short and
+`onPressStart` is called immediately.
+
+### onPressEnd: (e: PressEvent) => void
+
+Called once the element is no longer pressed. It will be cancelled if the press
+starts again before the `delayPressEnd` threshold is exceeded.
+
+### onPressChange: boolean => void
+
+Called when the element changes press state (i.e., after `onPressStart` and
+`onPressEnd`).
+
+### onLongPress: (e: PressEvent) => void
+
+Called once the element has been pressed for the length of `delayLongPress`.
+
+### onLongPressChange: boolean => void
+
+Called when the element changes long-press state.
+
+### onLongPressShouldCancelPress: () => boolean
+
+Determines whether calling `onPress` should be cancelled if `onLongPress` or
+`onLongPressChange` have already been called. Default is `false`.
+
+### onPress: (e: PressEvent) => void
+
+Called after `onPressEnd` only if `onLongPressShouldCancelPress` returns
+`false`.
+
+### delayPressStart: number
+
+The duration of a delay between when the press starts and when `onPressStart` is
+called. This delay is cut short if the press ends released before the threshold
+is exceeded.
+
+### delayPressEnd: number
+
+The duration of the delay between when the press ends and when `onPressEnd` is
+called.
+
+### delayLongPress: number = 500ms
+
+The duration of a press before `onLongPress` and `onLongPressChange` are called.
+
+### pressRententionOffset: { top: number, right: number, bottom: number, right: number }
+
+Defines how far the pointer (while held down) may move outside the bounds of the
+element before it is deactivated. Once deactivated, the pointer (still held
+down) can be moved back within the bounds of the element to reactivate it.
+Ensure you pass in a constant to reduce memory allocations.