bug#15899: 24.3.50; regression: `region' overlay is lower priority than default

[Dmitry Gutov <dgutov@yandex.ru>]

On 16.11.2013 13:24, Eli Zaretskii wrote:
> What way is that?  Before region highlighting was reimplemented as an
> overlay, it had a fixed "priority" that couldn't be controlled or
> worked around.  So what exactly did easy-kill expect from that
> behavior?

That behavior was broken on Leo Liu's system (don't know how) and on 
mine too (with some themes only).

See https://github.com/leoliu/easy-kill/issues/3 for more details.

> But the region always has point on one of its ends, so both the places
> where point was and where it is are clearly visible when the region is
> active.

In many times point wasn't at any of region ends. That's how `easy-mark' 
works, it selects some unit of text *around* the point.

> So why is there a need for the easy-mark to be visible in
> that situation (which is transient and therefore short-lived)?

Just for user information. Looks kinda nice.

> The part of the region that overlaps the easy-mark overlay will not be
> visible, if the region's priority is lower.

That just means that easy-mark will need to set its priority higher than 
the *documented* region priority.

> That's not the race I had in mind.  What I had in mind was users
> complaining about their favorite overlay-based features being obscured
> by the region, lobbying the maintainers to increase the priorities of
> those overlays above the region (and possibly also above the easy-mark
> overlay), or increase the priority of the region overlay; then other
> users complaining about the effects of that, and so on and so forth ad
> nauseam.

This will have to be solved on a package-by-package basis, like every 
contentious feature. One user complaint: change the priority of a 
package-specific overlay. More complaints to change it in different 
directions: add a user option that will set the priority that overlay.

 > How can you even assume that the "region overlay priority
> won't change", given the possibility and enough pressure from users?
> Once out of the bottle, this genie cannot be easily put back.

Region priority will have to be set once (to 100, or something), 
documented, and then never changed again. Any changes will have to be 
made to other overlays' priorities.