You could say that the bezel holds it in but there is more to it than that. There is a large spring behind the dash that holds pressure against a spring cup that has two little ears on it which fit into the two corresponding notches in the dash behind the bezel. The spring must be compressed (by grabbing hold of the swith body and pushing towards the dash), to cause the ears on the spring cup to stick thru the dash which in turn the bezel turns into the spring cup and is held in place with two internal ears of it's own.

I trust that is as clear as mud. Someone around here probably has a pic of this, wait awhile, it will show up.