(defun event-start (event)
"Return the starting position of EVENT.
-EVENT should be a mouse click, drag, or key press event.
+EVENT should be a mouse click, drag, or key press event. If
+EVENT is nil, the value of `posn-at-point' is used instead.
The following accessor functions are used to access the elements
of the position:
`posn-area': A symbol identifying the area the event occurred in,
or nil if the event occurred in the text area.
`posn-point': The buffer position of the event.
-`posn-x-y': The pixel-based coordiates of the event.
+`posn-x-y': The pixel-based coordinates of the event.
`posn-col-row': The estimated column and row corresponding to the
position of the event.
`posn-actual-col-row': The actual column and row corresponding to the