Emitted when has-tooltip is TRUE and the hover timeout has expired with the cursor hovering "above" widget; or emitted when widget got focus in keyboard mode.
Using the given coordinates, the signal handler should determine whether a tooltip should be shown for widget. If this is the case TRUE should be returned, FALSE otherwise. Note that if keyboard_mode is TRUE, the values of x and y are undefined and should not be used.
The signal handler is free to manipulate tooltip with the therefore destined function calls.