The XSetInputFocus(3) function changes the input
focus and the last-focus-change time. It has no effect if the
specified time is earlier than the current last-focus-change time
or is later than the current X server time. Otherwise, the
last-focus-change time is set to the specified time (CurrentTime is
replaced by the current X server time). XSetInputFocus(3)
causes the X server to generate FocusIn and FocusOut events.
Depending on the focus argument, the following occurs:
If focus is None, all keyboard events are discarded until a new
focus window is set, and the revert_to argument is
ignored.
If focus is a window, it becomes the keyboard's focus window.
If a generated keyboard event would normally be reported to this
window or one of its inferiors, the event is reported as usual.
Otherwise, the event is reported relative to the focus window.
If focus is PointerRoot, the focus window is dynamically taken
to be the root window of whatever screen the pointer is on at each
keyboard event. In this case, the revert_to argument is
ignored.
The specified focus window must be viewable at the time
XSetInputFocus(3) is called, or a BadMatch error
results. If the focus window later becomes not viewable, the X
server evaluates the revert_to argument to determine the new
focus window as follows:
If revert_to is RevertToParent, the focus reverts to the
parent (or the closest viewable ancestor), and the new
revert_to value is taken to be RevertToNone.
If revert_to is RevertToPointerRoot or RevertToNone, the
focus reverts to PointerRoot or None, respectively. When the focus
reverts, the X server generates FocusIn and FocusOut events, but
the last-focus-change time is not affected.
XSetInputFocus(3) can generate BadMatch,
BadValue, and BadWindow errors.
The XGetInputFocus(3) function returns the focus
window and the current focus state.
Some numeric value falls outside the range of values accepted
by the request. Unless a specific range is specified for an
argument, the full range defined by the argument's type is
accepted. Any argument defined as a set of alternatives can
generate this error.
BadWindow
A value for a Window argument does not name a defined
Window.