XEDIT (System Variable)
Controls whether the current drawing can be edited in-place when being referenced by another drawing.
XFADECTL (System Variable)
Controls the amount of fading within a reference being edited in place. This setting affects only the objects that are not being edited in the reference.
XLOADCTL (System Variable)
Turns xref demand-loading on and off, and controls whether it opens the referenced drawing or a copy.
XREFSTATE
Indicates whether the Reference Manager palette is open or closed, and can be used to toggle the display state of the Reference Manager palette.
XREFTYPE (System Variable)
Controls the default reference type when attaching or overlaying an external reference.