Controls the default reference type when attaching or overlaying an external reference.
| Type: | Integer | 
| Saved in: | Registry | 
| Initial value: | 0 | 
|  
			  Value  | 
 
			  Description  | 
|---|---|
|  
			  0  | 
 
			  Attachment is the default  | 
|  
			  1  | 
 
			  Overlay is the default  |