# File lib/sass/tree/root_node.rb, line 18
      def render
        Visitors::CheckNesting.visit(self)
        result = Visitors::Perform.visit(self)
        Visitors::CheckNesting.visit(result) # Check again to validate mixins
        result, extends = Visitors::Cssize.visit(result)
        result = result.do_extend(extends) unless extends.empty?
        result.to_s
      end