Using alt-key clicks on linux

[hh]

[I take the liberty to move this to a new thread in order to have a more
appropriate subject]

> Richard Gaskin wrote (in thread 'nice Sierra feature'):
>>> Mark Wieder wrote: 
>>> On linux you can alt-click to grab and move a window. 
> 
> ... which is both great and horrible. 
> It's handy, of course, but it also means not being able to rely on 
> Alt-click in our UIs. 
> In many cases I've migrated some Alt-click functionality to Shift-click, 
> but it's nice to have both mod keys available, and some things make more 
> semantic sense with Alt rather than Shift.

Because this is so important for a lot of Mac/Win/linux stacks, especially
linux-RaspberryPi, I use it there often (and let user's know in the help):

[1]
*** alt-mouseDown does NOT come through to LC.

[2]
*** alt-mouseUp works:
*** You have to FIRST click the object, THEN -- while the mouse is down --
*** hold the altKey down.

(Usually nearly everybody uses the reverse order: first the key then the click).
*** So one could say, "alt-click" on linux should be done as "click-alt" ***

Try it from a button with

on mouseUp
   put the optionkey into fld 1
end mouseUp

Tested on Ubuntu/Mint/Rapbian.