bug#56820: outline-minor-mode replacing the first character with an arrow

[Juri Linkov]

> This doesn't work well:
>
>   . moving the mouse pointer on and off the button causes horizontal
>     movement of both the arrow and the following character, the one
>     that was added to the overlay's 'display' string (I guess this
>     depends on the font used for the arrow characters?);
>   . one cannot put the cursor on the first character that's displayed
>     on the outline button
>
> I very much hope we can improve the visuals here, because otherwise
> the feature looks unfinished at best.
>
> Some related questions:
>
>   . do we really need to hide the first character of the line by the
>     overlay? doesn't before-string work?

Does using before-string allows moving the cursor into the button
displayed with before-string?

>   . wouldn't it be better if the arrow buttons were displayed in the
>     window's margin, and would thus avoid indenting the characters on
>     that line wrt the rest of the code?

Same problem: the cursor can't be moved into the fringe indicator
to be able to type RET on it.

>   . the buttons have a dark gray background that doesn't look good.

The buttons that I see by default are much worse - their background is
glaring orange.