https://learn.microsoft.com/en-us/dotnet/api/system.windows.drageventargs.allowedeffects?view=windowsdesktop-10.0
DragEventArgs.AllowedEffects Property (System.Windows) | Microsoft Learn
Gets a member of the DragDropEffects enumeration that specifies which operations are allowed by the originator of the drag event.
property systemwindowsmicrosoftlearn