Ask the user what to do with the data.
Copy the data.
Add a link to the data. Note that this is only useful if source and destination agree on what it means, and is not supported on all platforms.
Move the data, i.e. first copy it, then delete it from the source using the DELETE target of the X selection protocol.
No action.
Used in Gdk.Drop and Gdk.Drag to indicate the actions that the destination can and should do with the dropped data.