There are many public ones on chromium-dev and blink-dev, e.g. https://docs.google.com/document/d/1OjZoHNvn_vz6bhyww68B_KZB... linked from https://groups.google.com/a/chromium.org/g/blink-dev/c/POCUb.... (This is just the first one I found, I don’t know if it’s well-written.)