This command can be used when a family file (.rfa) is open in Revit.
Add Subcategories will prompt a new dialogue box to choose the subcategory list file. The list of subcategories comes from an external text file, which can be easily modified in accordance with company or country standards. The default list of subcategories comes from ANZRS. To see only the subcategories available for the current family category, remove the tick mark from 'Show All Categories'.
By clicking File, you can select a different file of subcategories.
After selecting the required subcategories and clicking OK, the data will be added to the family, where it can easily be assigned to solids.