doc: improve examples.

docs/content/middlewares/errorpages.md

@@ -49,7 +49,7 @@ labels:
 - "traefik.http.middlewares.test-errorpage.errors.query=/{status}.html"
 ```
 
-```toml tab="File"
+```toml tab="File (TOML)"
 # Custom Error Page for 5XX
 [http.middlewares]
   [http.middlewares.test-errorpage.errors]
@@ -61,6 +61,21 @@ labels:
   # ... definition of error-handler-service and my-service
 ```
 
+```yaml tab="File (YAML)"
+# Custom Error Page for 5XX
+http:
+  middlewares:
+    test-errorpage:
+      errors:
+        status:
+        - "500-599"
+        service: serviceError
+        query: "/{status}.html"
+
+[http.services]
+  # ... definition of error-handler-service and my-service
+```
+
 !!! note 
     In this example, the error page URL is based on the status code (`query=/{status}.html)`.