Selection tools : quickly switching between add/subtract

[Warren Baird]

Hey all,

Probably another noob question:   I'm in the process now of trying to 
use krita to extract objects like a flower from their background.   In 
Gimp I go to a 'lasso' tool, and then can easily switch between add and 
subtract by pressing a modifier like 'shift'.

I haven't been able to find any way to do the same thing in Krita 
without going and clicking somewhere, which is way too slow...

Am I just missing something?   Or do I need to do some coding?

Warren