External references, or xrefs, are files brought into AutoCAD drawings as attachments or overlays. The option to overlay or attach an xref is available under the Reference Type section of the Attach ...
xref is apparently new in Emacs 25, which I haven't used, so I can't test it out personally to see if the override actually works or is needed.
Some results have been hidden because they may be inaccessible to you
Show inaccessible results