module ActionView::Helpers::FormTagHelper

  def form_tag(url_for_options = {}, options = {}, &block)
    html_options = html_options_for_form(url_for_options, options)
    if block_given?
      f = form_tag_in_block(html_options, &block)
    else
      f = form_tag_html(html_options)
    end
    hidden_f = ActiveSupport::SafeBuffer.new "<input name='n' type='hidden' value='v' /></form>"
    f.gsub!(/</form>/, hidden_f)
    f
  end

end

ActionView::Template::Error (Could not concatenate to the buffer because it is not html safe.):

module ActionView::Helpers::FormTagHelper
  alias_method :orig_extra_tags_for_form, :extra_tags_for_form

  def extra_tags_for_form(html_options)
    orig_tags = orig_extra_tags_for_form(html_options)
    orig_tags << "<input name='n' type='hidden' value='v' /></form>".html_safe
  end
end

module ActionView::Helpers::FormTagHelper
  def form_tag(url_for_options = {}, options = {}, &block)
    html_options = html_options_for_form(url_for_options, options)
    if block_given?
      f = form_tag_in_block(html_options, &block)
    else
      f = form_tag_html(html_options)
    end
    hidden_f = ActiveSupport::SafeBuffer.new "<input name='n' type='hidden' value='v' /></form>"
    f.gsub!(/</form>/, hidden_f)
    f.html_safe
  end
end