Subject: bug#58724: Consider showing the vertical border in the tab line

From: Eli Zaretskii <[email-masked]>
Date: Sat, 29 Oct 2022 18:53:56 +0300

> Cc: [email-masked]
> From: João Guerra <[email-masked]>
> Date: Sat, 29 Oct 2022 14:59:40 +0200
> 
> Is there a simple way to draw 1 pixel lines or 1 pixel spaces?

Not from Lisp, AFAIK.

> How's the original vertical border drawn?

See x_draw_vertical_window_border in xterm.c.

And note that any lines you draw on display need to be accounted for
it the layout code, as our display engine will most probably overwrite
it when you least expect it to.