    # File lib/action_view/helpers/form_options_helper.rb, line 436
          def grouped_options_for_select(grouped_options, selected_key = nil, prompt = nil)
            body = ''
            body << content_tag(:option, prompt, :value => "") if prompt

            grouped_options = grouped_options.sort if grouped_options.is_a?(Hash)

            grouped_options.each do |group|
              body << content_tag(:optgroup, options_for_select(group[1], selected_key), :label => group[0])
            end

            body
          end