On Fri, Nov 13, 2015 at 9:32 AM, João Távora <address@hidden
> In fact, this pattern of multiple extensions/commands competing for a
> Emacs setting is relatively common, I wonder we could abstract some more
> generic solution...
Don't know about generic (meaning, not only margins), but it certainly would help to have a package/library/API/whatever to help packages coordinate use of the window margins.