Expire evars manually (within a server call)

[#1]

It would be good to be able to expire / empty an evar explicitly / manually.

Therefore it would be best to have a keyword (like eg. "Null") which can be set as a value for the evar, that leads to an instant clear of the value / expiration of that evar.

So if I have an evarX which contains a value I would like to be able submit evarX="null".

From that call onward this evar should behave as if it has never been set.

[#2]

One of the settings of an eVar is the expiration.  You can set the expiration to an event, and then set that event to manually expire the eVar.  Are you wanting to have the eVar expire after a visit by default, but then have an extra flag or variable you can set to expire it without having to use an event?  I think this would be great, since there may be multiple scenarios where you would want to expire an eVar, and not just after a visit.