The XIAllowEvents request releases some queued events if the client
has caused a device to freeze. It also is used to handle touch grab and
ownership processing.

The function has no effect if the specified time is earlier than the last-grab
time of the most recent active grab for the client, or if the specified time is
later than the current X server time. The time parameter must be CurrentTime for
requests with event modes of XIAcceptTouch and XIRejectTouch.

The following describes the processing that occurs depending on what constant
you pass to the event_mode argument:

XIAsyncDevice:
    If the specified device is frozen by the client, event processing for that
    device continues as usual. If the device is frozen multiple times by the
    client on behalf of multiple separate grabs, XIAsyncDevice thaws for
    all. XIAsyncDevice has no effect if the specified device is not frozen
    by the client, but the device need not be grabbed by the client.

XISyncDevice:
    If the specified device is frozen and actively grabbed by the client,
    event processing for that device continues normally until the next
    button press or release, or key press or release, or a gesture begin or end
    event (depending on the grab) is reported to the client.
    At this time, the specified device again appears to freeze.
    However, if the reported event causes the grab to be released, the
    specified device does not freeze.
    XISyncDevice has no effect if the specified device is not frozen by the
    client or is not grabbed by the client.

XIReplayDevice:
    If the specified device is actively grabbed by the client and is frozen
    as the result of an event having been sent to the client (either from
    the activation of a XIGrabButton or from a previous XIAllowEvents with
    mode SyncDevice, but not from a Grab), the grab is released and
    that event is completely reprocessed.  This time, however, the request
    ignores any passive grabs at or above (towards the root) the
    grab window of the grab just released.
    The request has no effect if the specified device is not grabbed by
    the client or if it is not frozen as the result of an event.
    In case of gesture begin event being replayed, the original grabbing
    client will receive a XI_GesturePinchEnd or XI_GestureSwipeEnd event.

XIAsyncPairedDevice:
    If the paired master device is frozen by the client, event processing
    for it continues as usual. If the paired device is frozen multiple
    times by the client on behalf of multiple separate grabs,
    XIAsyncPairedDevice thaws for all.
    XIAsyncPairedDevice has no effect if the device is not frozen by the
    client, but those devices need not be grabbed by the client.
    XIAsyncPairedDevice has no effect if deviceid specifies a slave device.

XISyncPair:
    If both the device and the paired master device are frozen by the
    client, event processing (for both devices) continues normally until
    the next XI_ButtonPress, XI_ButtonRelease, XI_KeyPress, or XI_KeyRelease
    event is reported to the client for a grabbed device (button event for
    a pointer, key event for a keyboard), at which time the devices again
    appear to freeze. However, if the reported event causes the grab to be
    released, then the devices do not freeze (but if the other device is
    still grabbed, then a subsequent event for it will still cause both
    devices to freeze).
    XISyncPair has no effect unless both the device and the paired master
    device are frozen by the client. If the device or paired master device
    is frozen twice by the client on behalf of two separate grabs,
    XISyncPair thaws for both (but a subsequent freeze for XISyncPair will
    only freeze each device once).
    XISyncPair has no effect if deviceid specifies a slave device.

XIAsyncPair:
    If the device and the paired master device are frozen by the client,
    event processing for both devices continues normally. If a device is
    frozen twice by the client on behalf of two separate grabs, AsyncBoth
    thaws for both. XIAsyncPair has no effect unless both the device and the
    paired master device frozen by the client.
    XIAsyncPair has no effect if deviceid specifies a slave device.

XIAcceptTouch:
    The client is deemed to have taken control of the touch sequence once it
    owns the sequence. TouchEnd events will be sent to all clients listening
    to the touch sequence that have either grabbed the touch sequence on a
    child window of the grab_window or have received events for the touch
    sequence through event selection. These clients will no longer receive
    any TouchUpdate events.

XIRejectTouch:
    The client is no longer interested in the touch sequence, and will
    receive a XI_TouchEnd event. If the client is the current owner of the
    sequence, ownership will be passed on to the next listener.

BadDevice
        An invalid deviceid was specified.

BadAccess
        This error may occur if event_mode is XIAcceptTouch and this client
        is not the current or potential owner of the specified touch ID.

BadValue
        This error may occur if event_mode is XIAcceptTouch and touch ID is invalid.

BadWindow
        A value for a grab_window argument does not name a defined
        Window.

XIGrabButton(3)