bug#39098: 26.3; bug of mouse-face including linebreak

[ynyaaa]

Eli Zaretskii <eliz@gnu.org> writes:

> tags 39098 notabug
> thanks
>
>> From: ynyaaa@gmail.com
>> Date: Sun, 12 Jan 2020 22:32:31 +0900
>> 
>> If 'mouse-face is put on a reaion including linebreaks and active,
>> the appearance of the blank areas right to linebreaks is changed.
>> But pointing the blank areas does not activate 'mouse-face.
>> 
>> If 'mouse-face is put on a region ending with a linebreak,
>> the activated appearance covers the first character of the next line.
>
> This is not a bug, this is how mouse-face is supposed to work.  It
> differs from other faces in this regard, because it is intended to be
> used to show mouse-sensitive text, including text that spans multiple
> lines.

Why is the out-of-range character highlighted only if it is at the
beginning of line?