How to add docked item?

The docked items can be docked to either on the top,
right, left, or bottom of a panel (both form and window components are subclasses
of panel).

dockedItems: [{
   xtype: 'toolbar',
   items: [{ 
      id:'buttonId', 
      handler: function() { 
         Ext.Msg.alert('title','alertMsg');
      });
   }]
}]