Re: visual-line-mode produces erratic behaviour with text properties

[Eli Zaretskii]

> From: Paul Rankin <hello@paulwrankin.com>
> Date: Fri, 01 Jul 2016 18:29:40 +1000
> 
> On Fri, 1 Jul 2016, at 05:55 PM, Eli Zaretskii wrote:
> > Super-long lines such as this one slow down the display engine, and
> > there are various redisplay optimizations to try to countermand that,
> > so perhaps this is one of them.
> 
> Do you mean Emacs has redisplay optimisations that may be causing the erratic 
> navigation?

Yes, at least in principle.

> Or, are there redisplay optimisations I can implement myself in an affected 
> major mode to work around this?

That's not the way to deal with these problems.  If some redisplay
optimization causes incorrect display in some use case, it should be
disabled in that use case.  IOW, it's a bug that needs to be fixed,
not worked around in application code.

> > In general, my recommendation is to stay away of such long lines in
> > Emacs.
> 
> I can't control this for users of the major mode. It's an edge case, but 
> still.

That recommendation was mainly for end-users, not for developers.  Of
course, if you can come up with an implementation that avoids long
lines, you as developer should prefer it, but I understand this is not
such a case.