are you talking about a kind of data overlay? like notes on top of notes, with highlight areas marked by start and end?

it's not that complicated to do this, a little complications as it really should refer to the character positions in the escaped json text to be uniform, so essentially "eventID, start, end" rinse and repeat

there is a NIP for this afaik, i think NIP-32  

 most relays will already accept such events it's more a problem of clients both creating them and showing them 

 https://github.com/nostr-protocol/nips/blob/master/84.md 

 I'm working on a PR for it. I ♥️ this NIP. It's such a big step, referring to parts of notes.

I don't think anyone sees the potential, but it's going to be one of the core NIPs. 

 is there some reason why it can't extend labels?