Intercept messages
 

What would be a good way to check a message before it is shown in the chat box and decide whether it should be shown or discarded?

ChatFrame_AddMessageEventFilter can be used to filter unwanted messages from the chat frame.

If what you want to do can't be done with that you can overwrite the chat frame's AddMessage function, but the other method is preferable.

That seems to work for my needs, thank you very much!