    # File lib/action_view/helpers/asset_tag_helper.rb, line 770
              def expand_sources
                if @sources.include?(:all)
                  assets = all_asset_files
                  ((defaults.dup & assets) + assets).uniq!
                else
                  expanded_sources = validate_sources!
                  expanded_sources << APPLICATION_JS if include_application?
                  expanded_sources
                end
              end