Export to DWG - "Merging Reference"?

When we export DGN>DWG files, Microstation presents a progress bar and information stating "Merging Reference....", and when complete; "Merge of 1 Reference(s) Complete"
What is the relevance of both the words Reference and Merge? My files have no References attached - all I'm doing is exporting from one format to another.
Why not simply "Exporting File: Filename.dgn > DWG"? and "Export to DWG Complete"?

Just curious,


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