RegisterChatCallback binds a function to some chat system event in order to affect the behavior of the Lua chat system. The first argument determines the event (using the ChatCallbackType enum) to which the second argument, the function, shall be bound. The default Lua chat system uses Chat/InvokeChatCallback|InvokeChatCallback to invoke registered functions. Attempting to register a server- or client- only callback on a peer that isn’t a server or client respectively will raise an error. The following sections describe in what ways registered functions will be used.

OnCreatingChatWindow

Client-only. Invoked before the client constructs the chat window. Must return a table of settings to be merged into the information returned by the ChatSettings module.

OnClientFormattingMessage

Client-only. Invoked before the client displays a message (whether it is a player chat message, system message, or /me command). This function is invoked with the message object and may (or may not) return a table to be merged into message.ExtraData.

OnClientSendingMessage

Not invoked at this time.

OnServerReceivingMessage

Server-only. Invoked when the server receives a message from a speaker (note that speakers may not necessarily be a Player chatting). This callback is called with the Message object. The function can make changes to the Message object to change the manner in which the message is processed. The Message object must be returned for this callback to do anything. Setting this callback can allow the server to, for example:

• Set message.ShouldDeliver to false in order to cancel delivery of the message to players (useful for implementing a chat blacklist)
• Get/set the speaker’s name color (message.ExtraData.NameColor, a Color3) on a message-by-message basis