bug#9159: 24.0.50; `undo' is not as good as it should be wrt property changes

[Lars Magne Ingebrigtsen]

"Drew Adams" <drew.adams@oracle.com> writes:

> I already said in the OP that "while correct" (N.B.) "it would be
> better for the property `foo' to simply be removed."

I don't think this is a bug (or should be fixed), but I wonder whether
it would make sense for Fput_text_property to just delete the property
instead of adding/setting `prop nil' to the property list in general?

That is, if I say

(put-text-property (point-min) (1+ (point-min)) 'foo nil)

today, `foo nil' is added.  Perhaps it should just be ignored if not
already there, and if it's already set, then it should be removed?

If we have established that there is no semantic difference between nil
properties and missing properties, then this sounds like there could be
(very minor) memory and redisplay efficiencies to be won here.

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