# File lib/sass/script/functions.rb, line 2507
    def selector_extend(selector, extendee, extender)
      selector = parse_selector(selector, :selector)
      extendee = parse_selector(extendee, :extendee)
      extender = parse_selector(extender, :extender)

      extends = Sass::Util::SubsetMap.new
      begin
        extender.populate_extends(extends, extendee)
        selector.do_extend(extends).to_sass_script
      rescue Sass::SyntaxError => e
        raise ArgumentError.new(e.to_s)
      end
    end