Re: Question about copy-region-as-kill

[Richard Stallman]

    If we had extents like mechanism as the underlying implementation of
    both text properties and overlays, then I could fall back to just using
    the raw extents interface to solve my problem.

That would be indistinguishable in practice form using overlays for
everything.  It would not be terribly hard to do this, but if indeed
overlays are slower, then this will make everything that now uses text
properties slower.

Are overlays actually slower, for something like font-lock?
I don't know.

      I agree with you that text properties and
    overlays cover the majority of cases, but I think there is something
    more fundamental lying behind both of them.

I don't think overlays (whether you call them "extents" or not)
are lying behind text properties.