Simple question. I was about to assign the Ctrl+Alt++ keyboard shortcut to increase the volume, but I then realized it was already assigned for something. If I press this key combination the screen flashes black for a second, and then comes back. Pressing Ctrl+Alt+- produces similar behavior. So I'm curious, what's this shortcut supposed to do?
Ctrl + Alt + F1 through F12 are mapped for switching between virtual consoles. Your graphical display is usually mapped to
vt8, so F7 or F8.
Ctrl + Alt + BkSp aborts your graphical server and kills all graphical processes.
Ctrl + Alt + - and + switch to a smaller or higher screen resolution, respectively.
Ctrl + Alt + Esc runs
xkill by default. The next window you click is killed.
There are several others, but I can't recall them.
If you want to map +/- to something, I'd suggest using the Windows key as a modifier, if you have one. It's treated as a "Super" Meta-key, and doesn't normally have any mappings at all.