REFSET command
Adds or removes entities from the reference (block or xref) being edited.
                Icons: 

Description
Transfers objects between the RefEdit working set and host drawing.
Note: This command can be used only after the REFEDIT command
                    has commenced.
            Options
- Add
 - Adds entities from the drawing to the reference being edited.
 
- Remove
 - Removes entities from the reference being edited; removed entities are placed in the drawing. Entities not in the reference are shown in gray.