Proposal for BiDi in terminal emulators

[Eli Zaretskii via Unicode]

> Date: Tue, 29 Jan 2019 13:50:31 +0100
> From: Egmont Koblinger via Unicode <unicode at unicode.org>
> 
> [1] https://terminal-wg.pages.freedesktop.org/bidi/

Interesting document, thanks for writing it.

My personal experience with bringing BiDi to Emacs led me to a firm
conclusion that BiDi support by terminal emulators cannot be relied on
by sophisticated text editing and display applications that are
BiDi-aware.  The terminal emulator can never be smart enough to do
what the editing needs require, so the application eventually ends up
jumping through hoops in order to trick the terminal into doing TRT.
It is easier to tell users to disable BiDi support of the terminal (if
it even has one), and do everything in the app.  This is the only way
of having full control of what is displayed, especially when
"higher-level protocols" need to be used to tailor the UBA to the need
of the user, because there's usually no way of asking the terminal to
apply a behavior which deviates from the UBA.

(If needed, I can provide examples of subtle problems with using BiDi
support of a terminal in BiDi-aware editing.  Not sure this will be
interesting to too many readers of this forum, though.)