code: function() {
              var tip = this.tip;
              if (!tip) {
                  tip = this.tip = Ext.create('Ext.tip.QuickTip', {
                      ui: 'form-invalid'
                  });
                  tip.tagConfig = Ext.apply({}, {attribute: 'errorqtip'}, tip.tagConfig);
              }
          }
docs: Use a custom QuickTip instance separate from the main QuickTips singleton, so that we
  can give it a custom frame style. Responds to errorqtip rather than the qtip property.
  @static