OffchainMessageContentFormat
A restriction on what characters the message text can contain and how long it can be.
The aim of this restriction is to make a message more likely to be signable by a hardware wallet that imposes limits on message size. In the case of wanting a message to be clear-signable, restricting the character set to ASCII may ensure that certain models of hardware wallet without extended character sets can display it onscreen.
Remarks
This only applies to v0 messages.