bug#41856: mouse-drag-copy-region: mention where it is talking about

[積丹尼 Dan Jacobson]

mouse-drag-copy-region is a variable defined in ‘mouse.el’.
Its value is nil

    Documentation:
    If non-nil, copy to kill-ring upon mouse adjustments of the region.

    This affects ‘mouse-save-then-kill’ (<mouse-3>) in
    addition to mouse drags.

OK, but mention if it is talking only about mouse actions within emacs,
or even elsewhere too.