I don't think the sed syntax was implemented in an effort to make a good interface; rather, they simply implemented what many (albeit technical) users have been

I don't think the sed syntax was implemented in an effort to make a good interface; rather, they simply implemented what many (albeit technical) users have been writing for years. I've been using sed-like notation to chat with colleagues for years. HipChat just chose to do something about it. I believe you could also edit your last message with the mouse, or by pressing "up" (but I don't remember if that was opt-in).