code: function(xtype) {
          var me = this;
  
          if (Ext.isArray(xtype)) {
              Ext.Array.forEach(xtype, me.addXTypeToWhitelist, me);
              return;
          }
  
          if (!Ext.Array.contains(me.whitelist, xtype)) {
              me.whitelist.push(xtype);
          }
      }
docs: Adds the specified xtype to the {@link #whitelist}.
  @param {String/String[]} xtype Adds the xtype(s) to the {@link #whitelist}.