Fixes #168: Added "Overriding error handler from a module" recipe

Author: samdark

book/README.md

@@ -18,6 +18,7 @@ Logging and error handling
 - Customizing 404 page
 - Handling errors and exceptions
 - Understanding error stack trace
+- [Overriding error handler from a module](overriding-error-handler-from-a-module.md)
 
 Web essentials
 --------------

book/overriding-error-handler-from-a-module.md

@@ -0,0 +1,32 @@
+# Overriding error handler from a module
+
+In some cases you want a custom error handler to be used for particular module.
+
+Yii doesn't have support for module-based error handling. The error handler is
+global i.e. there's only one for the whole application that is already registered
+by the time a module is executed. Therefore we need to both overwrite `errorHandler`
+component, set it for a current application and register it as a PHP error handler.
+Here's how to do it:
+
+```php
+class Module extends \yii\base\Module
+{
+    public function init()
+    {
+        parent::init();
+        \Yii::configure($this, [
+            'components' => [
+                'errorHandler' => [
+                    'class' => ErrorHandler::className(),
+                ]
+            ],
+        ]);
+
+        /** @var ErrorHandler $handler */
+        $handler = $this->get('errorHandler');
+        \Yii::$app->set('errorHandler', $handler);
+        $handler->register();
+    }
+}
+```
+