Drag & Dropping
Dropping a Blueprint class Actor into a viewport will add the Actor to the scene. When successfully dragging a Class, the mouse will show what class is in hand. Only one class can be dragged at a time.
Besides dropping into the viewport, classes can be dropped into combo boxes in the details window. Only classes that are children of the class associated with the combo box may be successfully dropped. An example is the World Properties details window and the GameMode Override where dropping any child class of GameMode will work.
Classes that have not been loaded will not appear in the combo box. Dropping a class into the combo box will force load the class.