Just like with XREFs, I'd like to be able to specify a reference type for a DREF: attachment or overlay. When XREFing multiple phases of a project together, you can use overlays to show the progress up to the current phase.
For example:
Phase 0.dwg:
Contains survey COGO points; existing features linework; and existing ground surface (Surf-PH0_EG).
Phase 1.dwg:
Contains XREF overlay of Phase 0.dwg (for PH0 linework); DREF of Surf-PH0_EG; PH1 proposed linework and surface (Surf-PH1_PR); and composite surface (Surf-PH1_COMB; set to No_Display surface style) from pasting Surf-PH1_PR over Surf-PH0_EG. User has to freeze/hide Surf-PH0_EG XREF layer from Phase 0.dwg to prevent display overlap with the DREF of Surf-PH0_EG, but no biggie.
So far, so good, but the next step is where it gets messy and my proposal would come into play.
Phase 2.dwg
Contains XREF overlay of Phase 0.dwg (for PH0 linework); XREF overlay of Phase 1.dwg (for PH1 linework); DREF of Surf-PH1_COMB (surface style changed to EG/background surface style); PH2 proposed linework and surface (Surf-PH2_PR); and composite surface (Surf_PH2-COMB; set to No_Display surface style) from pasting Surf-PH2_PR over Surf-PH1_COMB.
User has to freeze/hide:
Surf-PH0_EG XREF layer from Phase 0.dwg AND
Surf-PH0_EG XREF layer from Phase 1.dwg (resulting from DREF) AND
Surf-PH1_PR XREF layer from Phase 1.dwg.
If the user could specify DREF of Surf-PH0_EG in Phase 1.dwg as an overlay, then they wouldn't have to worry about it showing up in Phase 2.dwg.
