improved doc.

docs/api/base/Component.md

+Component is the base class that implements the *property*, *event* and *behavior* features.
+
 Component provides the *event* and *behavior* features, in addition to the *property* feature which is implemented in
 its parent class [[Object]].
 

docs/api/base/Object.md

+Object is the base class that implements the *property* feature.
+
 A property is defined by a getter method (e.g. `getLabel`), and/or a setter method (e.g. `setLabel`). For example,
 the following getter and setter methods define a property named `label`:
 
@@ -30,4 +32,30 @@ $object->label = 'abc';
 If a property has only a getter method and has no setter method, it is considered as *read-only*. In this case, trying
 to modify the property value will cause an exception.
 
-One can call [[hasProperty]], [[canGetProperty]] and/or [[canSetProperty]] to check the existence of a property.
+One can call [[hasProperty()]], [[canGetProperty()]] and/or [[canSetProperty()]] to check the existence of a property.
+
+
+Besides the property feature, Object also introduces an important object initialization life cycle. In particular,
+creating an new instance of Object or its derived class will involve the following life cycles sequentially:
+
+1. the class constructor is invoked;
+2. object properties are initialized according to the given configuration;
+3. the `init()` method is invoked.
+
+In the above, both Step 2 and 3 occur at the end of the class constructor. It is recommended that
+you perform object initialization in the `init()` method because at that stage, the object configuration
+is already applied.
+
+In order to ensure the above life cycles, if a child class of Object needs to override the constructor,
+it should be done like the following:
+
+~~~
+public function __construct($param1, $param2, ..., $config = array())
+{
+    ...
+    parent::__construct($config);
+}
+~~~
+
+That is, a `$config` parameter (defaults to `array()`) should be declared as the last parameter
+of the constructor, and the parent implementation should be called at the end of the constructor.

framework/base/Component.php

@@ -10,12 +10,7 @@ namespace yii\base;
 use Yii;
 
 /**
- * Component is the base class that provides the *property*, *event* and *behavior* features.
- *
  * @include @yii/base/Component.md
- *
- * @property Behavior[] behaviors list of behaviors currently attached to this component
- *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */

framework/base/Object.php

@@ -8,10 +8,7 @@
 namespace yii\base;
 
 /**
- * Object is the base class that provides the *property* feature.
- *
  * @include @yii/base/Object.md
- *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */