# File lib/sass/selector/sequence.rb, line 109
      def do_extend(extends, parent_directives, replace, seen, original)
        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, replace, seen)

          # The First Law of Extend says that the generated selector should have
          # specificity greater than or equal to that of the original selector.
          # In order to ensure that, we record the original selector's
          # (`extended.first`) original specificity.
          extended.first.add_sources!([self]) if original && !has_placeholder?

          extended.map {|seq| seq.members}
        end
        weaves = Sass::Util.paths(extended_not_expanded).map {|path| weave(path)}
        trim(weaves).map {|p| Sequence.new(p)}
      end