Kinda depends on whether you're asking for Wikimedia-specific rules or general MediaWiki rules.
Speaking just about Wikimedia, each local wiki community may have different preferences. There is no process for enforcing global (meaning, cross-wiki) recommendations in this regard, so in practice, even if someone from the technical community came up with universal rules, no one would really need to stick to them, and if they did and their contribution was reverted, the argument from these rules could be ignored.
Best,
