Custom client scope mappers

Hello all,
I am writting some custom oidc client mappers. The logic of mapping is clear, but there is a magic in configuration. Many mappers contains static method “create(arg1, …)”. When is this method called? Where are arguments taken from? I have found solution to override method “validateConfig(…)” where I am able to set default values. But is it the right place? Or is there some documentation on this topic? Thanks for any advice.