bug#46621: Copy line

[Drew Adams]

> > * A single-key binding (like H-y but not C-x y) makes quite
> > a difference because that way I can quickly stutter out copies as
> > needed without having to plan ahead and use prefix arguments.
> 
> I don't believe everyone would agree on such short keys.
> Maybe better to try finding a key in the 'C-x x' keymap
> (that already contains a line-related binding 'C-x x t'
> `toggle-truncate-lines').

Please take all proposals of new default key bindings
to emacs-devel.

And I'd suggest not making any suggestions of new
bindings for _new_ commands.  That's premature UI
"optimization".