Edited existing content, sketched out "Creating Your Own Behavior"

Undoubtedly will need to update “Creating Your Own Behavior” to reflect
changes in Yii 2.

docs/guide/behaviors.md

@@ -1,16 +1,16 @@
 Behaviors
 =========
 
-A behavior (also knows as mixin) can be used to enhance the functionality of an existing component without modifying its
-code. In particular, it can "inject" its own methods and properties into the component and make them directly accessible
-via the component. It can also respond to the events triggered in the component and thus intercept the normal
-code execution. Unlike PHP traits, behaviors could be attached to classes at runtime.
+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
+via the component itslef. 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.
 
 Using behaviors
 ---------------
 
-Behavior can be attached to any class that extends from `Component`. In order to do so you need to implement `behaviors`
-method. Yii provides `AutoTimestamp` behavior that handles updating timestamp fields on saving active record model.
+A behavior can be attached to any class that extends from `Component`. In order to attach a behavior to a class, the component class must implement the `behaviors`
+method. As an example, Yii provides the `AutoTimestamp` behavior for automatically updating timestamp fields when saving an Active Record model:
 
 ```php
 class User extends ActiveRecord
@@ -32,10 +32,59 @@ class User extends ActiveRecord
 }
 ```
 
-In the above `class` value is a string containing fully qualified behavior class name. All the other key-values are
-assigned to corresponding properties of the class.
+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 `AutoTimestamp` class, thereby customizing how the behavior functions.
 
 Creating your own behaviors
 ---------------------------
 
-TBD
+[[NEEDS UPDATING FOR Yii 2]]
+
+To create your own behavior, you must define a class that implements the `IBehavior` interface. This can be accomplished by extending `CBehavior`. More specifically, you can extend `CModelBehavior` or `CActiveRecordBehavior` for behaviors to be used specifically with models or with Active Record models. 
+
+```php
+class MyBehavior extends CActiveRecordBehavior
+{
+}
+```
+
+To make your behavior customizable, like `AutoTimestamp`, add public properties:
+
+```php
+class MyBehavior extends CActiveRecordBehavior
+{
+	public $attr;
+}
+```
+
+Now, when the behavior is used, you can set the attribute to which you'd want the behavior to be applied:
+
+```php
+class User extends ActiveRecord
+{
+	// ...
+
+	public function behaviors()
+	{
+		return [
+			'mybehavior' => [
+				'class' => 'ext\mybehavior\MyBehavior',
+				'attr' => 'member_type'
+				],
+			],
+		];
+	}
+}
+```
+
+Behaviors are normally written to take action when certain model-related events occur, such as `beforeSave` or `afterFind`. You can write your behaviors to have the corresponding method. Within the method, you can access the model instance through `$this->getOwner()`:
+
+```php
+class MyBehavior extends CActiveRecordBehavior
+{
+	public $attr;
+	public function beforeSave() {
+		$model = $this->getOwner();
+		// Use $model->$attr
+	}
+}
+```