[Boost-users] Why is _internal_weak_this public in enable_shared_from_this?

I can see why you might want to make it protected and have it friend the shared_ptr template (because it does the initialization of _internal_weak_this I think), but I don't see any obvious reason for it to be public. Can anyone explain? You can see the relevant code here: http://www.boost.org/doc/libs/1_38_0/boost/enable_shared_from_this.hpp