This message will be posted to the application queue associated with the window that has the focus, or with the window that is to receive the pointer-button information.

WM_PICKUP message is sent to the window under the mouse pointer when the user presses the direct-manipulation button while holding down the lazy drag augmentation key, currently the ALT key. This message is used to inform an application that the user is commencing a lazy drag operation. The container control sends its owner a CN_PICKUP notification when it receives a message.

Objects are added to the drag set when a WM_PICKUP message is received. The first time the message is received, the application initiates a lazy drag operation. Each subsequent WM_PICKUP message that is received during the course of the lazy drag operation indicates that objects are to be added to the drag set.