module T::Private::Abstract::Hooks

def prepended(other)

It will get called when *that* module gets prepended in another class/module.
This will become the self.prepended method on a module that extends Abstract::Hooks. 
def prepended(other)
ending abstract methods is weird. You'd only be able to override them via other prepended
les, or in subclasses. Punt until we have a use case.
.raise "Prepending abstract mixins is not currently supported."