Please refer to the Spec:
https://docs.google.com/document/d/1AbdKXHmlLxofl2N-AJQOBVFXfgAa4kwrsd0fQTpp2-4/edit
other internal docs
https://docs.google.com/document/d/1042NMnPUA4mdXO5IGkEjIL0KXmzsVJ8tmcsU617Mdbk/edit?ts=5d56b17e#
Doc describing catgories:
https://docs.google.com/document/d/1iSLJ7t4YzyoCWssLHI7d0mI97kBkMfeICwTZA-ZFGhg/edit
direct links to hep documents:
https://drive.google.com/file/d/0B9-LAjOGdvsTUmRtWFVWZ0hGRnZSQm96X3NXZEh0aTdXTUVn/view
https://drive.google.com/file/d/0B9-LAjOGdvsTRU1fbnJTTkVFcEtYdVB1T080RE5nTlB0ZEhz/view