Hello Emacs,

adaptive-wrap is a GNU ELPA package that adds a wrap-prefix property to
continuation lines to make them look like they have been filled with
M-q.  For example, it makes this…

    ; Here is a long Elisp comment
    with its continuation line.

… look like this:

    ; Here is a long Elisp comment
    ; with its continuation line.

The second "; " is not part of the buffer text: it is the wrap-prefix
computed by adaptive-wrap.  This prefix can be customized with the
integer variable adaptive-wrap-extra-indent, which adds (if positive) or
takes off (if negative) some extra padding.

In bug#41810, I tried to tackle the following issues:

1. The extra-indent character is not fontified:
<https://debbugs.gnu.org/cgi/bugreport.cgi?att=1;bug=41810;filename=1-extra-indent.png;msg=5>

2. The prefix has no background, which makes lines with :extend'ed
   backgrounds visually jarring:
<https://debbugs.gnu.org/cgi/bugreport.cgi?msg=5;filename=2-extend-t-current.png;bug=41810;att=3>

I proposed (and Stefan and Basil kindly reviewed) two patches:

1. One to fix those two bugs: