The ALERT-C protocol is designed to provide mostly event-oriented road end-user information messages. Many "hooks" have been left for future development and indeed a few status-orientated road end-user information messages were included. The presentation section of the ALERT-C protocol specifies messages that may be presented to the user in accordance with the general requirements set out above. It defines the message structure and content, and its presentation to the end-user. The ALERT-C protocol utilises a standardised Event List) of event messages with their code values, which also includes general traffic problems and weather situations. Being transmitted as a series of codes, RDS-TMC messages are language-independent and can be presented in the language of the user's choice. ALERT-C defines two categories of information within messages: basic and optional items. In principle, basic information is present in all messages. Optional information can be added to messages where necessary. Standard RDS-TMC user messages provide the following five basic items of explicit, broadcast information: 1. Event description, giving details of road event situation, general traffic problems and weather situations (e.g. congestion caused by an accident) and where appropriate its severity (e.g. resulting queue length). 2. Location, indicating the area, road segment or point location where the source of the problem is situated. 3. Direction and Extent, identifying the adjacent segments or specific point locations also affected by the incident, and where appropriate the direction of traffic affected. 4. Duration, giving an indication of how long the problem is expected to last. 5. Diversion advice, showing whether end-users are recommended to find and follow an alternative route. Optional information can be added to any message using one or more additional RDS data groups. This optional addition can give greater detail or can deal with unusual situations. Any number of additional fields can in principle be added to each basic message, subject only to a maximum message length of five RDS data groups.