A WebKitUserMessage is a message that can be used for the communication between the UI process and web extensions. A WebKitUserMessage always has a name, and it can also include parameters and UNIX file descriptors. Messages can be sent from a #WebKitWebContext to all #WebKitWebExtension<!-- -->s, from a #WebKitWebExtension to its corresponding #WebKitWebContext, and from a #WebKitWebView to its corresponding #WebKitWebPage (and vice versa). One to one messages can be replied to directly with webkit_user_message_send_reply().