Idea: units of insertion.

[RMS at MIT-AI (Richard M. Stallman)]

Imagine that inserting a character starts a "unit of insertion".
While a unit of insertion is in progress, the bounds of the insertion
are remembered.  Moving the cursor outside those bounds ends the unit
of insertion, and the next insertion starts a new unit.

Then, there could be a command to copy the text of the last unit
of insertion into the kill ring, or into the buffer at point.
Or to kill th last unit of insertion.

This is an attempt to get the useful feature, which editors with
explicit insert commands have, that you can refer to the string which
was the argument of te last insert command, to insert it again, etc.

As lon as yo keep editing within the unit of insertion, or inserting
next to it, the same unit continues.

Do you think this is a useful idea?