field_set_tag (ActionView::Helpers::FormTagHelper)

    # File lib/action_view/helpers/form_tag_helper.rb, line 408
          def field_set_tag(legend = nil, &block)
            content = capture(&block)
            concat(tag(:fieldset, {}, true), block.binding)
            concat(content_tag(:legend, legend), block.binding) unless legend.blank?
            concat(content, block.binding)
            concat("</fieldset>", block.binding)
          end