bug#38013: [PATCH] Rectangular region selection with mouse

["Mattias Engdegård" <mattiase@acm.org>]

1 nov. 2019 kl. 08.51 skrev Eli Zaretskii <eliz@gnu.org>:

> Could you please tell how to try and test this feature?  The patch
> comes without any documentation, so it's hard to understand quickly
> what to do to see this in action.

With the default settings, click and drag (mouse button 1) with meta held to mark a rectangular region.
Sorry about the lack of documentation; it will be written once we agree on the design.

> I'd prefer not to step on another feature, if possible.  How about
> defining a minor mode, and then using the usual mouse selection
> gestures instead?  That would be more natural, IMO, and will not
> require users to give up another feature.

Very much agree that other features should be left alone, but in this case there seemed to be no really good unused binding.
A minor mode is less ideal: rectangular selection is something the user wants to be able to do on a whim, without having to plan ahead by activating a minor mode. It is also good to follow standard practice in other editors and terminal emulators

Competing mouse bindings are:

Meta: secondary selection
Shift: mouse-appearance-menu (mouse-save-then-kill for NS)
Control: mouse-buffer-menu

The secondary selection appeared weaker than the rest, in the sense that repurposing its binding would annoy fewer users than the alternatives. (Annoyed users can still regain the old behaviour by customisation.)

Other possibilities:

A. Unbind mouse-appearance-menu, mouse-save-then-kill or mouse-buffer-menu instead. The trade-offs are similar.
B. Combined modifiers (Shift-Meta etc). Less ergonomic; there may be platform restrictions.
C. Use a different mouse button. Diverges from other platforms; messy on Macs.
D. Less common modifiers (Super, Hyper). Many don't have them.
E. Follow the platform conventions. Not the Emacs tradition, and makes for more binding clashes.
F. Leaving rectangular selection unbound by default. This is tantamount to stating that it is less useful. Is it?