Perhaps I should be a bit clearer. When I said the "level 3" approach "appears to be inline with the direction Victor Stinner is going in for PEP 511", it was mostly at a superficial level. Meaning: - PEP 511 still appears to use integer (unnamed) optimization levels for alternate transformers (fat 0, 1, and 2). I assumed (perhaps incorrectly) that you could provide a list of transformers ("opt,fat,bar") but that each transformer would still contain a number of different off/on toggles, arbitrarily identified as integer flags like 0, 1, and 2. I should go back and read that PEP again. I don't recall seeing where the 0, 1, and 2 came from in the fat examples. os.cpython-36.fat-0.pyc os.cpython-36.fat-1.pyc os.cpython-36.fat-2.pyc - Secondly, I reviewed PEP 511 when I initially started working on the naive "level 3" approach to make sure what I proposed didn't impede the progress of PEP 511 (or more realistically make my attempt obsolete). Since PEP 511 didn't seem to deviate much from the current integer flags (aside from allowing multiple different named sets of integer flags), I figured that whatever approach PEP 511 took with the existing optimization levels (0, 1, and 2) would presumably also work for a new level 3. I hope that makes sense... If not, let me know & I'll try again tomorrow to be clearer. PS. I think it sounds like I'm now re-advocating for the simple "level 3" approach. I'm not – just trying to explain my earlier thought process. I'm open to all kinds of feedback & suggestions. Thanks again folks! Cheers, --diana