Used in GdkDragContext to indicate what the destination should do with the dropped data.
|Copy the data.
|Move the data, i.e. first copy it, then delete it from the source using the DELETE target of the X selection protocol.
|Add a link to the data. Note that this is only useful if source and destination agree on what it means.
|Special action which tells the source that the destination will do something that the source doesn't understand.
|Ask the user what to do with the data.