The primary option is the preferred design option in the set. Elements in the main model and in the primary option can reference each other.
Only one design option in a set can be the primary option. All other options are secondary. By default, each project view displays both the main model and the primary option for each set.
If you want to promote a secondary option to be the primary option, be aware that Revit attempts to move relationships from the former primary option to the new primary option. For example, suppose you create a dimension from a main model wall to a primary option wall. In a secondary option, the same wall has been moved slightly. When you promote the secondary option to be the primary option, Revit displays the same dimension between the main model wall and the moved wall. The dimension is updated to show the correct distance between the walls.
To promote a secondary option to be the primary option
Revit promotes the selected secondary option to be the primary option. The Design Options dialog lists the design option with (primary) after its name. The former primary option is now a secondary option.