User-defined attributes in DGN files
A tag is a user-defined textual attribute that may or may not be displayed visually in a DGN file. Tags are linked to a host DGN element.
An MSLink is a named nongraphic data element that serves as a primary key for linking a graphic element to an external database.
ArcGIS translates an MSLink as a field and a value in the feature class attribute table. The external data that is referenced by the MSLink can also be added to ArcMap and appended to the feature layer attribute table using the Join dialog box.