class Sass::Selector::Sequence

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 && !invisible?
    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