BOLT 12 is an upgrade that aims to enhance user experience and privacy. It introduces features such as re-usable payment requests, increased receiver privacy, and better censorship resistance. BOLT 12 allows for more flexible and extensible ways to structure and exchange data, making it easier to add new features and improvements without disrupting existing implementations 

 What do you mean by "flexible and extensible ways to structure and exchange data"? Can I send a text message with my payment now, or no? 

 Yes, but technically you always could.

Because you fetch an invoice, that invoice contains the message. And now you can prove that you wrote the message, and that the recipient received the message: the invoice they sign has your message in it, and your key (often a made up one for that payment). 

 Interesting. Is there a limit to the message length? I'm thinking about using this for live streaming super chats. 

 The total length needs to fit in 64k, so yes. But the other fields tend to be no more than a few kB... 

 Thanks for the replies and all of the hard work!