docs: function showPanel(on){
          var fc_rules = $('#fc_rules');
          if (!fc_rules.length) {
              fc_rules = $('<style id="fc_rules"><\/style>').appendTo('head');
          }
          fc_rules.text(!on ? "" : " #tool_topath { display: none !important; }");
          $('#polygon_panel').toggle(on);
      }