Make the callback example more similar to the new API

content/docs/refs-and-the-dom.md

@@ -267,18 +267,25 @@ All things considered, we advise against exposing DOM nodes whenever possible, b
 
 React also supports another way to set refs called "callback refs", which give more fine-grain control over when refs are set and unset.
 
-Instead of passing a `ref` attribute created by `createRef()`, you pass a function. The function receives the React component instance or HTML DOM element as its argument, which can be stored and accessed elsewhere. This example uses the `ref` callback to store a reference to a DOM node:
+Instead of passing a `ref` attribute created by `createRef()`, you pass a function. The function receives the React component instance or HTML DOM element as its argument, which can be stored and accessed elsewhere. 
+
+The example below implements a common pattern: using the `ref` callback to store a reference to a DOM node in an instance property.
 
 ```javascript{6,17}
 class CustomTextInput extends React.Component {
   constructor(props) {
     super(props);
+    this.textInput = { value: null }; // initial placeholder for the ref
     this.focusTextInput = () => {
-      // Explicitly focus the text input using the raw DOM API
-      this.textInput.focus();
+      // Focus the text input using the raw DOM API
+      this.textInput.value.focus();
     };
   }
 
+  componentDidMount () {
+    if (this.textInput) this.focusTextInput() // autofocus the input on mount
+  }
+
   render() {
     // Use the `ref` callback to store a reference to the text input DOM
     // element in an instance field (for example, this.textInput).
@@ -286,7 +293,7 @@ class CustomTextInput extends React.Component {
       <div>
         <input
           type="text"
-          ref={(input) => { this.textInput = input; }} />
+          ref={element => this.textInput.value = element} />
         <input
           type="button"
           value="Focus the text input"
@@ -300,8 +307,6 @@ class CustomTextInput extends React.Component {
 
 React will call the `ref` callback with the DOM element when the component mounts, and call it with `null` when it unmounts. `ref` callbacks are invoked before `componentDidMount` or `componentDidUpdate` lifecycle hooks.
 
-Using the `ref` callback to set a property on the class is a common pattern for accessing DOM elements. The preferred way is to set the property in the `ref` callback like in the above example. There is even a shorter way to write it: `ref={input => this.textInput = input}`. 
-
 You can pass callback refs between components like you can with object refs that were created with `React.createRef()`.
 
 ```javascript{4,13}