The above page does not exist. The EnumItems are instead listed on the RegisterChatCallback page. That being said, it’s not explicitly stated that the list below the explanation of the method contains the ChatCallbackTypes - you have to make that logical assumption yourself.
I feel that it would be more appropriate to fill in this page with information rather than to leave it blank. People like me sometimes click the type that a parameter expects and it’d be unfortunate to be led to a blank page.