Applications should support the system topic at all times. This topic provides a context for information that may be of general interest to another application.
Data-item values must be rendered in the CF_TEXT clipboard format. Individual elements of item values for a system topic must be delimited by tab characters. The following table suggests some items for the system topic.
| Item | Description |
|---|---|
| Formats | Tab-delimited list of clipboard formats the application can render. Typically, CF_ formats are listed with the "CF_" portion of the names removed (for example, CF_TEXT is listed as "TEXT"). |
| Help | Text that briefly explains how to use the DDE server. |
| 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. |
| SysItems | List of system-topic items the application supports. |
| TopicItemList | Similar to the SysItems item, except that TopicItemList should be supported for each topic other than the system topic. This allows browsing of the items supported under any topic. If the items cannot be enumerated, this item should contain only "TopicItemList". |
| Topics | List of topics the application supports at the current time; this list can vary from moment to moment. |