doc update about behavior.

docs/guide/behaviors.md

@@ -2,7 +2,7 @@ Behaviors
 =========
 
 A behavior (also knows as *mixin*) can be used to enhance the functionality of an existing component without modifying the component's
-code. In particular, a behavior can "inject" its own methods and properties into the component, making them directly accessible
+code. In particular, a behavior can "inject" its public methods and properties into the component, making them directly accessible
 via the component itself. A behavior can also respond to  events triggered in the component, thus intercepting the normal
 code execution. Unlike [PHP's traits](http://www.php.net/traits), behaviors can be attached to classes at runtime.
 
@@ -11,10 +11,12 @@ Using behaviors
 
 A behavior can be attached to any class that extends from [[yii\base\Component]]. In order to attach a behavior to a class,
 the component class must implement the `behaviors`
-method. As an example, Yii provides the [[yii\behaviors\AutoTimestamp|AutoTimestamp]] behavior for automatically updating timestamp
+method. As an example, Yii provides the [[yii\behaviors\TimestampBehavior]] behavior for automatically updating timestamp
 fields when saving an [[yii\db\ActiveRecord|Active Record]] model:
 
 ```php
+use yii\behaviors\TimestampBehavior;
+
 class User extends ActiveRecord
 {
 	// ...
@@ -23,7 +25,7 @@ class User extends ActiveRecord
 	{
 		return [
 			'timestamp' => [
-				'class' => 'yii\behaviors\AutoTimestamp',
+				'class' => TimestampBehavior::className(),
 				'attributes' => [
 					ActiveRecord::EVENT_BEFORE_INSERT => ['created_at', 'updated_at'],
 					ActiveRecord::EVENT_BEFORE_UPDATE => 'updated_at',
@@ -34,9 +36,38 @@ class User extends ActiveRecord
 }
 ```
 
-In the above, the `class` value is a string representing the fully qualified behavior class name.
-All of the other key-value pairs represent corresponding public properties of the [[yii\behaviors\AutoTimestamp|AutoTimestamp]]
-class, thereby customizing how the behavior functions.
+In the above, the name `timestamp` can be used to reference the behavior through the component. For example, `$user->timestamp`
+gives the attached timestamp behavior instance. The corresponding array is the configuration used to create the
+[[yii\behaviors\TimestampBehavior|TimestampBehavior]] object.
+
+Besides responding to the insertion and update events of ActiveRecord, `TimestampBehavior` also provides a method `touch()`
+that can assign the current timestamp to a specified attribute. As aforementioned, you can access this method directly
+through the component, like the following:
+
+```php
+$user->touch('login_time');
+```
+
+If you do not need to access a behavior object, or the behavior does not need customization, you can also
+use the following simplified format when specifying the behavior,
+
+```php
+use yii\behaviors\TimestampBehavior;
+
+class User extends ActiveRecord
+{
+	// ...
+
+	public function behaviors()
+	{
+		return [
+			TimestampBehavior::className(),
+			// or the following if you want to access the behavior object
+			// 'timestamp' => TimestampBehavior::className(),
+		];
+	}
+}
+```
 
 
 Creating your own behaviors
@@ -54,7 +85,7 @@ class MyBehavior extends Behavior
 }
 ```
 
-To make it customizable, like [[yii\behaviors\AutoTimestamp]], add public properties:
+To make it customizable, like [[yii\behaviors\TimestampBehavior]], add public properties:
 
 ```php
 namespace app\components;