http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSDraggingInfo_Protocol/

Constants that are returned by draggingSourceOperationMask

*NSDragOperationCopy - The data represented by the image can be copied. *NSDragOperationLink - The data can be shared. *NSDragOperationGeneric - The operation can be defined by the destination. *NSDragOperationPrivate - The operation is negotiated privately between the source and the destination. *NSDragOperationMove - The data can be moved. *NSDragOperationDelete - The data can be deleted. *NSDragOperationEvery - All of the above. *NSDragOperationNone - No drag operations are allowed.

(The following lines are from NSDragging.h)

/* protocol for the sender argument of the messages sent to a
drag destination. The view or window that registered dragging types sends these messages as dragging is happening to find out details about that session of dragging. */ @protocol NSDraggingInfo

• (NSWindow *)draggingDestinationWindow;
• (NSDragOperation)draggingSourceOperationMask;
• (NSPoint)draggingLocation;
• (NSPoint)draggedImageLocation;
• (NSImage *)draggedImage;
• (NSPasteboard *)draggingPasteboard;
• (id)draggingSource;
• (int)draggingSequenceNumber;
• (void)slideDraggedImageTo:(NSPoint)screenPoint; @end