but there is no restriction being goobally applied in nostr, nostr is just a standard protocol. The only reason it’s standarised is to enable compatibility between similar clients. You are not obligated to follow this though. You can post in your own relay, use your own event kinds or even stop following standard rules. They are not imposed by force. You can go to France and start speaking Russian… but do not expect people to follow or understand. Freedom of speech doesn’t work without freedom of listening.