title: In extjs4 how to set focus of textfield
body: <p>I am working in extjs4. i have activation view form as-
  <img src="https://i.stack.imgur.com/SZm9U.png" alt="enter image description here"></p>
  
  <p>For entering key i have taken item as-</p>
  
  <pre><code>{
                  margin:'5 5 5 5',
                  xtype: 'fieldcontainer',
                  fieldLabel: 'Enter key',
                  layout: 'hbox',
                  combineErrors: true,
                  defaults: {
                      hideLabel: true
                  },
                  items: [{xtype: 'textfield',    fieldLabel: 'a', name: 'a', width: 80,  allowBlank:false, margins: '0 5 0 0'},
                  {xtype: 'textfield',    fieldLabel: 'b', name: 'b', width: 80, allowBlank: false, margins: '0 5 0 0'},
                  {xtype: 'textfield',    fieldLabel: 'c', name: 'c', width: 80, allowBlank: false, margins: '0 5 0 0'},
                  {xtype: 'textfield',    fieldLabel: 'd', name: 'd', width: 80, allowBlank: false, margins: '0 5 0 0'},
                  {xtype: 'textfield',    fieldLabel: 'e', name: 'e', width: 80, allowBlank: false, margins: '0 5 0 0'}]},
  </code></pre>
  
  <p>I want to restrict number of characters in each block to 5. And after entering 5 char in first block,i want to set focus to next block automatically. So how to implement this in extjs4</p>