# File lib/sass/selector/sequence.rb, line 80
      def do_extend(extends, parent_directives, seen = Set.new)
        extended_not_expanded = members.map do |sseq_or_op|
          next [[sseq_or_op]] unless sseq_or_op.is_a?(SimpleSequence)
          extended = sseq_or_op.do_extend(extends, parent_directives, seen)
          choices = extended.map {|seq| seq.members}
          choices.unshift([sseq_or_op]) unless extended.any? {|seq| seq.superselector?(sseq_or_op)}
          choices
        end
        weaves = Sass::Util.paths(extended_not_expanded).map {|path| weave(path)}
        Sass::Util.flatten(trim(weaves), 1).map {|p| Sequence.new(p)}
      end