X/Xlib programming questions

[Erez D]

hello

i want to send keyboard and mouse event to a window at position x,y.
i thought of using XSendEvent

how do i find which is the top most window at pos x,y (without moving
the pointer position) ?
what fields do i need to fill in the event i send via XSendEvent,
i guess event.xbutton.serial and event.xbutton.send_event and
event.xbutton.display are filled automatically by xlib. am i correct ?

thanks,
erez.