response formatting docs about JSON configuration

close #11399

docs/guide/rest-response-formatting.md

@@ -155,3 +155,33 @@ Content-Type: application/json; charset=UTF-8
     }
 }
 ```
+
+### Controlling JSON output
+
+The JSON response is generated by the [[yii\web\JsonResponseFormatter|JsonResponseFormatter]] class which will
+use the [[yii\helpers\Json|JSON helper]] internally. This formatter can be configured with different options like
+for example the [[yii\web\JsonResponseFormatter::$prettyPrint|$prettyPrint]] option, which is useful on development for
+better readable responses, or [[yii\web\JsonResponseFormatter::$encodeOptions|$encodeOptions]] to control the output
+of the JSON encoding.
+
+The formatter can be configured in the [[yii\web\Response::formatters|formatters]] property of the `response` application
+component in the application [configuration](concept-configuration.md) like the following:
+
+```php
+'response' => [
+    // ...
+    'formatters' => [
+        \yii\web\Response::FORMAT_JSON => [
+            'class' => 'yii\web\JsonResponseFormatter',
+            'prettyPrint' => YII_DEBUG, // use "pretty" output in debug mode
+            'encodeOptions' => JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE,
+            // ...
+        ],
+    ],
+],
+```
+
+When returning data from a database using the [DAO](db-dao.md) database layer all data will be represented
+as strings, which is not always the expected result especially numeric values should be represented as
+numbers in JSON. When using the ActiveRecord layer for retrieving data from the database, the values for numeric
+columns will be converted to integers when data is fetched from the database in [[yii\db\ActiveRecord::populateRecord()]].