Layer 2 Management Link (L2ML) messages

When we have SAPI=63 at layer 2 then at layer 3 we have Layer 2 Management Link (L2ML). I have searched a lot to find L2ML messages or any document or standard stating that but didnt get that. Please help in this regard. I have seen many documents explaining RSL at layer3 (SAPI=0) but neither of the documents discuss the scenerio when SAPI=63.