This message is posted to the target of a drop when F1 is pressed during a direct-manipulation operation, and the drag operation is canceled.

The usOperation field of pDraginfo can be used to provide help information in the context of the drag operation during which it was requested.

The DM_DROPHELP message is not supported for lazy drag operations. Since the drag operation is non-modal, the user may request help on anything at any time during the drag. If the application wishes to provide drop help, it must specify the action required to invoke drop help (for example a menu choice), and code the support for it explicitly.