A mature open source project may be governed under an open source foundation which usually gives it a charter https://github.com/cncf/foundation/blob/main/charter.md#3-va...

... and/or set of values: https://kubernetes.io/community/values/

There's also a lot of open source guides here https://todogroup.org/resources/guides/ that may help you if you're looking at building mature open source projects.