MessageType property represents the message type e.g. "Sdl.FileTypeSupport.Filters.Verifiers.QAChecker.ProcessorNumbers; Extra number in target segment." The message type string should be unique for each message so it should refer to specific messages and not broad classes of messages. This message type property is optional and can be null but it is recommended that the message type is supplied. It is important to note that the MessageType property is not intended to be displayed to the user and should not be localised.