A drag and drop operation occurs when the user clicks and holds the mouse button in a pane supporting dragging, then drags to a pane supporting dropping, and releases the mouse button.
Visual feedback may be provided indicating that dragging is happening, whether a drop operation is possible at the current mouse position, and what operation will occur when the user drops. Usually the operation is the transfer of data.
You need to decide which CAPI pane(s) and interfaces will support dragging and then implement it for each, and similarly for dropping. You will implement drag and drop for one or more specified data formats.
CAPI User Guide and Reference Manual (Macintosh version) - 3 Aug 2017