I'm trying to to have a visible mark depicting the "state" the buffer is at.
A "state" is nothing more but a function that sets or unsets some keymapings that should be easily arbitrarily turned on or of on a per buffer basis.
I'm looking for a way to show some visual mark for every buffer that has that state set. Something like this (with ASCII graphics):
For example, pressing
F4 draw that little rectangle in the top, and repressing it clears it.
It doesn't have to be that exact visual mark, am open to suggestions that are simpler to implement but clearly show a visual difference in the buffer.
Any suggestions on how to do this?