As far as I know, support library is using because old devices don't have new APIs. For example they don't know what Fragment is and how to implement it. Therefore, these behaviors are defined in support library.
So, my main question is, what is/are difference(s) between library of Fragment in support library with its twin which is introduced in API 11 (Android v3.0, Honeycomb).
My second question is, If its possible to put every new API in support library, why we have two types of libraries? I mean Android can release all APIs just under support library rather than support library and Android version X.xx library.