In fact, bind is only a simplified version of the
where HTk.html#HTk.WishEventModifierWishEventModifier desribes possible event modifiers such as Shift, Alt, Meta (corresponding to the Shift, Alt or Meta key being held), Button1, ..., Button5 (corresponding to mouse button 1 thru 5 being pressed) or Double and Triple. Again, not all combinations of modifiers and events make sense; for example, double and triple pertain to mouse button presses, and modifying a mouse button press with a different button is not really helpful. Note that the argument of bind is a list of events, meaning that the interface events have to occur in (rapid) sequence to generate the event.
Here, the first component of the return value is an event of
EventInfo, which is a labelled record as
The information here is the x and y component of the mouse position, both relative to the window in which the event occurs, and the root window (i.e. the screen), and the button being pressed.