For the most part, messages issued at interactive terminals (like TSO/E and CICS® terminals) are documented by the specific elements and products that support those terminals.
This information also contains the routing and descriptor codes that IBM® assigns to the messages that z/OS® components, subsystems, and products issue. Routing and descriptor codes are specified by the ROUTCDE and DESC keyword parameters on WTO and WTOR macros, which are the primary methods that programs use to issue messages. The routing code identifies where a message will be displayed. The descriptor code identifies the significance of the message and the color of the message on operator consoles with color.
The MVS™ System Messages documents are cumulative. As messages are added to the system they are added to the documents. Similarly, when messages are changed on the system, they are changed in the documents. However, when a message is deleted from the system (no longer issued), the message is not deleted from the document. This means that users can look in the most recent message documents for the most current descriptions of system messages.