bug#27544: 25.1; Visualization of Unicode bidirectional marks

[Itai Berli]

> This is how Emacs behaves, again in line with general Emacs feature of 
> allowing users to see what's in the buffer.

Except the current display doesn't allow the user to see what's in the buffer.

 > The UBA also allows to retain these characters, including display
them, see section 5.2 there.

Well, section 5.2 of the UBA explains:

> retention of these formatting characters and BNs is important to users who 
> need to display a graphic representation of hidden characters, and who thus 
> need to obtain their visual positions for display.

Emacs users who need to display a graphic representation of the bidi
marks are ill-served by the current implementation. And so are those
who don't need to display a graphic representation of them. The
current implementation is the worse of both worlds.