Added "Using controller action to render errors"

docs/guide/error.md

@@ -5,3 +5,52 @@ Error handling in Yii is different from plain PHP. First of all, all non-fatal e
 you can use `try`-`catch` to work with these. Second, even fatal errors are rendered in a nice way. In debug mode that
 means you have a trace and a piece of code where it happened so it takes less time to analyze and fix it.
 
+Using controller action to render errors
+----------------------------------------
+
+Default Yii error page is great for development mode and is OK for production if `YII_DEBUG` is turned off but you may
+have an idea how to make it more suitable for your project. An easiest way to customize it is to use controller action
+for error rendering. In order to do so you need to configure `errorHandler` component via application config:
+
+```php
+return [
+    // ...
+    'components' => [
+        // ...
+        'errorHandler' => [
+            'errorAction' => 'site/error',
+    ],
+```
+
+After it is done in case of error Yii will launch `SiteController::actionError()`. Since errors are converted to
+exceptions we can get exception from error handler:
+
+```php
+public function actionError()
+{
+    $exception = \Yii::$app->getErrorHandler()->exception;
+    $this->render('myerror', ['message' => $exception->getMessage()]);
+}
+```
+
+Since most of the time you need to adjust look and feel only, Yii provides `ErrorAction` class that can be used in
+controller instead of implementing action yourself:
+
+```php
+public function actions()
+{
+    return [
+        'error' => [
+            'class' => 'yii\web\ErrorAction',
+        ],
+    ];
+}
+```
+
+After defining `actions` in `SiteController` as shown above you can create `views/site/error.php`. In the view there
+are three varialbes available:
+
+- `$name`: the error name
+- `$message`: the error message
+- `$exception`: the exception being handled
+