Maybe these are on the to do list, if they are then sorry I must have missed them when I looked, if they are not then this is a new feature request.
Possibly I am not alone in that when I type a chat message, read it to confirm it is what I intended to say, sometimes spell check it, then send it; immediately on pressing send (keyboard enter/return) I notice yet another spelling mistake or on occasion an important word missing.
It would be really useful to have 1) the ability to edit previous messages and 2) to have the ability to recall (rescind) or delete (rescind) your last message.
The ability to edit or delete previous messages would be very useful if this were possible for any message sent in the current connected session.
In addition it would be useful to have 3) the ability to use the keyboard up or down arrows in the chat text entry box to recall a previous message from the current session to allow edit before sending it again as a new message.