guide WIP [skip ci]

docs/guide/extend-creating-extensions.md

@@ -3,7 +3,7 @@ Extending Yii
 
 > Note: This section is under development.
 
-The Yii framework was designed to be easily extendable. Additional features can be added to your project and then reused, either by yourself on other projects or by sharing your work as a formal Yii extension.
+The Yii framework was designed to be easily extensible. Additional features can be added to your project and then reused, either by yourself on other projects or by sharing your work as a formal Yii extension.
 
 Code style
 ----------

docs/guide/extend-customizing-core.md

-Helper Classes
-==============
-
-> Note: This section is under development.
-
-Yii provides many classes that help simplify  common coding tasks, such as string or array manipulations,
-HTML code generation, and so forth. These helper classes are organized under the `yii\helpers` namespace and
-are all static classes (meaning they contain only static properties and methods and should not be instantiated).
-
-
-You use a helper class by directly calling one of its static methods:
-
-
-```
-use yii\helpers\ArrayHelper;
-
-$c = ArrayHelper::merge($a, $b);
-```
-
-Extending Helper Classes
-------------------------
-
-To make helper classes easier to extend, Yii breaks each helper class into two classes: a base class (e.g. `BaseArrayHelper`)
-and a concrete class (e.g. `ArrayHelper`). When you use a helper, you should only use the concrete version, never use the base class.
-
-If you want to customize a helper, perform the following steps (using `ArrayHelper` as an example):
-
-1. Name your class the same as the concrete class provided by Yii, including the namespace: `yii\helpers\ArrayHelper`
-2. Extend your class from the base class: `class ArrayHelper extends \yii\helpers\BaseArrayHelper`.
-3. In your class, override any method or property as needed, or add new methods or properties.
-4. Tell your application to use your version of the helper class by including the following line of code in the bootstrap script:
-
-```php
-Yii::$classMap['yii\helpers\ArrayHelper'] = 'path/to/ArrayHelper.php';
-```
-
-Step 4 above will instruct the Yii class autoloader to load your version of the helper class instead of the one included in the Yii distribution.
-
-> Tip: You can use `Yii::$classMap` to replace ANY core Yii class with your own customized version, not just helper classes.

docs/guide/extend-using-composer.md

@@ -22,6 +22,20 @@ curl -s http://getcomposer.org/installer | php
 
 We strongly recommend a global composer installation.
 
+Installing Composer Class Autoloader
+------------------------------------
+
+Make sure the [entry script](concept-entry-scripts.md) of your application contains the following lines of code:
+
+```php
+// install Composer's class autoloader
+require(__DIR__ . '/../vendor/autoload.php');
+
+// include Yii class file
+require(__DIR__ . '/../vendor/yiisoft/yii2/Yii.php');
+```
+
+
 Working with composer
 ---------------------
 
@@ -52,7 +66,7 @@ composer.phar update
 
 As an example, packages on `dev-master` will constantly get new updates when you run `update`, while running `install` won't, unless you've pulled an update of the `composer.lock` file.
 
-There are several paramaters available to the above commands. Very commonly used ones are `--no-dev`, which would skip packages in the `require-dev` section and `--prefer-dist`, which downloads archives if available, instead of checking out repositories to your `vendor` folder.
+There are several parameters available to the above commands. Very commonly used ones are `--no-dev`, which would skip packages in the `require-dev` section and `--prefer-dist`, which downloads archives if available, instead of checking out repositories to your `vendor` folder.
 
 > Composer commands must be executed within your Yii project's directory, where the `composer.json` file can be found.
 Depending upon your operating system and setup, you may need to provide paths to the PHP executable and
@@ -100,7 +114,7 @@ afterwards.
 > Depending on the package additional configuration may be required (eg. you have to register a module in the config), but autoloading of the classes should be handled by composer.
 
 
-Using a specifc version of a package
+Using a specific version of a package
 ------------------------------------
 
 Yii always comes with the latest version of a required library that it is compatible with, but allows you to use an older version if you need to.

docs/guide/helper-overview.md

@@ -3,14 +3,26 @@ Helpers
 
 > Note: This section is under development.
 
-Helper classes typically contain static methods only and are used as follows:
+Yii provides many classes that help simplify common coding tasks, such as string or array manipulations,
+HTML code generation, and so on. These helper classes are organized under the `yii\helpers` namespace and
+are all static classes (meaning they contain only static properties and methods and should not be instantiated).
+
+You use a helper class by directly calling one of its static methods, like the following:
 
 ```php
-use \yii\helpers\Html;
+use yii\helpers\Html;
+
 echo Html::encode('Test > test');
 ```
 
-There are several classes provided by framework:
+> Note: To support [extending helper classes](#extending-helper-classes), Yii breaks each core helper class
+  into two classes: a base class (e.g. `BaseArrayHelper`) and a concrete class (e.g. `ArrayHelper`).
+  When you use a helper, you should only use the concrete version and never use the base class.
+
+
+## Core Helper Classes
+
+The following core helper classes are provided in the Yii releases:
 
 - ArrayHelper
 - Console
@@ -25,3 +37,39 @@ There are several classes provided by framework:
 - StringHelper
 - Url
 - VarDumper
+
+
+## Extending Helper Classes
+
+To custom a core helper class (e.g. `yii\helpers\ArrayHelper`), you should extend from its corresponding base class
+(e.g. `yii\helpers\BaseArrayHelper`) and name your class the same as the corresponding concrete class
+(e.g. `yii\helpers\ArrayHelper`), including its namespace.
+
+The following example shows how to customize the [[yii\helpers\ArrayHelper::merge()|merge()]] method of the
+[[yii\helpers\ArrayHelper]] class:
+
+```php
+namespace yii\helpers;
+
+use yii\helpers\BaseArrayHelper;
+
+class ArrayHelper extends BaseArrayHelper
+{
+    public static function merge($a, $b)
+    {
+        // your custom implementation
+    }
+}
+```
+
+Save your class in a file named `ArrayHelper.php`. The file can be in any directory, such as `@app/components`.
+
+Next, in your application's [entry script](structure-entry-scripts.md), add the following line of code
+after including the `yii.php` file:
+
+```php
+Yii::$classMap['yii\helpers\ArrayHelper'] = 'path/to/ArrayHelper.php';
+```
+
+The above line instructs the [Yii class autoloader](concept-autoloading.md) to load your version of the helper
+class, instead of the one included in the Yii releases.