bug#27103: Should show-trailing-whitespace highlight specified spaces?

[Clément Pit--Claudel]

On 2017-05-27 15:42, Eli Zaretskii wrote:
>> Cc: 27103@debbugs.gnu.org
>> From: Clément Pit--Claudel <clement.pitclaudel@live.com>
>> Date: Sat, 27 May 2017 15:14:00 -0400
>>
>> Would it be a reasonable feature request to ask for a non-replacing version 
>> of left-fringe and right-fringe?
> 
> I'm not sure.  Non-replacing specs are those which affect the way the
> text having the display property is displayed, but you want something
> else: a portion of text that is both displayed normally and produces
> the fringe bitmap.  That's not how display properties work.
> 
> IOW, it looks like implementing something like that will need serious
> changes in how the display engine works, because it basically
> traverses across a given buffer position only once.

Makes sense, thanks for the detailed explanation. Would the same caveat apply 
to the creation of a new 'left-fringe text property, such that instead of 
(concat "A" (propertize "_" 'display '(left-fringe filled-square))) one could 
write (propertize "A" 'left-fringe 'filled-square)?

Thanks,
Clément.

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