Bidi paragraph direction in terminal emulators

[Eli Zaretskii via Unicode]

> From: Elias Mårtenson <lokedhs at gmail.com>
> Date: Sat, 9 Feb 2019 13:33:49 +0800
> Cc: Egmont Koblinger <egmont at gmail.com>, unicode <unicode at unicode.org>
> 
>  Moreover, emitting the control sequences that set the mode is in
>  itself a complication, because if the terminal doesn't support them,
>  the result could be corrupted display.  You will need methods of
>  detecting the support, and those detection methods usually involve
>  sending another control sequence to the terminal and waiting for
>  response, something that complicates applications and causes delays in
>  displaying output.
> 
> That's what the TERM environment variable is for though.

That's not indicative enough when some version of a terminal starts to
support a feature not supported by previous versions of the same
terminal.  Happens a lot with terminal emulators such as xterm, which
are under active development, and add features all the time.