# File lib/sass/selector/comma_sequence.rb, line 26
      def resolve_parent_refs(super_cseq, implicit_parent = true)
        if super_cseq.nil?
          if contains_parent_ref?
            raise Sass::SyntaxError.new(
              "Base-level rules cannot contain the parent-selector-referencing character '&'.")
          end
          return self
        end

        CommaSequence.new(Sass::Util.flatten_vertically(@members.map do |seq|
          seq.resolve_parent_refs(super_cseq, implicit_parent).members
        end))
      end