show XML syntax for @ApiProperty(identifier=true) (#1250)

Author: yivi

core/identifiers.md

@@ -9,6 +9,7 @@ To help with your development experience, we introduced an identifier normalizat
 
 Let's say you have the following class, which is identified by a `UUID` type. In this example, `UUID` is not a simple string but an object with many attributes.
 
+[codeSelector]
 ```php
 <?php
 namespace App\Entity;
@@ -32,6 +33,15 @@ final class Person
 }
 ```
 
+```xml
+<resources xmlns="https://api-platform.com/schema/metadata">
+    <resource class="App\EntityPerson">
+        <property name="code" identifier="true"/>
+    </resource>
+</resources>
+```
+[/codeSelector]
+
 Once registered as an `ApiResource`, having an existing person, it will be accessible through the following URL: `/people/110e8400-e29b-11d4-a716-446655440000`.
 Note that the property identifying our resource is named `code`.