Applications are encouraged to support the System topic at all times. This topic provides a context for items of information that may be of general interest to another application.
Data-item values should be rendered in CF_TEXT format. Individual elements of item values for a System topic should be delimited by tab characters. Suggested items for the System topic include:
| Item | Description |
| SysItems | List of System-topic items supported by the application. |
| Topics | List of topics supported by the application at the current time; this list can vary from moment to moment. |
| ReturnMessage | Supporting detail for the most recently used WM_DDE_ACK message. This item is useful when more than eight bits of application-specific return data are required. |
| Status | Indication of the current status of the application. When a server receives a WM_DDE_REQUEST message for this System-topic item, it should respond by posting a WM_DDE_DATA message with a string containing either Busy or Ready, as appropriate. |
| Formats | List of clipboard format numbers that the application can render. |