Proposal for BiDi in terminal emulators

Eli Zaretskii via Unicode unicode at
Thu Jan 31 09:26:41 CST 2019

> Date: Thu, 31 Jan 2019 10:58:54 +0100
> Cc: unicode at
> From: Egmont Koblinger via Unicode <unicode at>
> Yes, I do argue that emacs will need to print a new escape sequence.
> Which is much-much-much-much-much better than having to tell users to
> go into the settings of their macOS Terminal / Konsole /
> gnome-terminal etc. and disable BiDi there, isn't it?

I'm not sure I agree.  Most users can disable bidi reordering of the
terminal once and for all.  They don't need it.

If terminals supported some control sequence to turn on and off the
reordering, it might be a useful feature to support such sequences.
But IME just querying the emulator whether it supports that or not is
a hassle, and generally slows down the application startup.  So it's a
mixed blessing.

> > On the other hand, all that the program can output is a sequence of Unicode
> > codepoints.  These don't include shaping information
> With "presentation form" characters, yes, they can, they do including
> shaping information.

Let's please stop talking about presentation forms, they solve only a
small part of the shaping problem.

> > and it's
> > the terminal who's equipped with _most_ of the needed data
> Why? It's the app that knows the context characters, it's the app that
> knows the language.

But only the emulator knows which fonts it uses, and only the emulator
can access the information about the font, like what OTF features it
supports, what glyphs it has, etc.

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