Subject: bug#51550: 29.0.50; Customize Group INS buttons sometimes don't have a left box line

From: Eli Zaretskii <[email-masked]>
Date: Wed, 29 Dec 2021 14:56:55 +0200

> From: Po Lu <[email-masked]>
> Cc: [email-masked],  [email-masked],  [email-masked]
> Date: Wed, 29 Dec 2021 08:33:22 +0800
> 
> Thanks for the explanation, it was very helpful.  Maybe it would work to
> put some kind of zero-width character with no face between the start of
> the line and the INS buttons?

I think it might be easier to use invisible text, assuming it does the
job.  For example, try this slightly modified variant of your recipe,
to see what I mean:

 (insert #("foo\n foo " 0 4 (face widget-field) 4 5 (invisible t) 5 8 (face custom-button)))