hello everyone 
I’m new to this board, so I’d first tell how glad I am to see so much nice people and interesting stuff!
then, a question about characters rigging:
I’ve found some .blend files where, by moving a slider bone, you can switch between IK and FK animation mode (see mancandy)
I saw that moving the slider, the influence value of other bones’ constraints will change:
well, I understand the constraints meaning, but I still don’t get how to make it so the bone’s position changes the influence value
may anyone explain or give me a link please?
thanks 