Commit to fix in Merlin-beta (need to finalize new merlin APIs before
beta is released).
See Comments for a long email containing my summary of the issue.
It sounds as though the solution people want is a new constructor
for MouseEvent with a new field: button.
Fortunately, we already have an excellent getter method for this field:
We decided to add a new ctor to InputEvent, MouseEvent, and KeyEvent
containing a field for the DOWN modifers. The MouseEvent ctor will also need
a field for the button that initiated the event (replaces the CHANGED masks).
We'll also need a getter method for the new field that carries the DOWN modifers.
When we do this, we'll need to update the docs about the new and old modifiers.
The docs should also warn developers that not all mice have three buttons,
and that they should write code that provides an alternate way of emulating
three button mice. (This task is for Sharon, with help from us.)