bug#49247: 28.0.50; [Feature Request] Make tab-bar-lines dragable

[Juri Linkov <juri@linkov.net>]

>> I actually don't quite see how to implement it even if it wasn't hard:
>> dragging the frame by its title bar or the external border is
>> implemented in the window manager, not in Emacs.  What would be the
>> way of implementing something similar in Emacs?
>
> See section 30.4.3.7 Mouse Dragging Parameters of the Elisp manual.

This is an impressive feature - it works like in window managers.

The only difference is that after trying

  (set-frame-parameter nil 'drag-with-header-line t)

then dragging is limited only to the screen boundaries
and doesn't allow dragging parts of the frame off the screen
(to leave frame partly visible) like window managers do.

Also can't drag by the mode-line with

  (set-frame-parameter nil 'drag-with-mode-line t)

but probably because it affects only frames without minibuffer window.

So it seems it should be possible to do the same for tab-line by implementing

  (set-frame-parameter nil 'drag-with-tab-line t)