mention that data is json array in supportsTransformation (input)

Author: soyuka

core/dto.md

@@ -78,7 +78,13 @@ final class BookInputDataTransformer implements DataTransformerInterface
      */
     public function supportsTransformation($data, string $to, array $context = []): bool
     {
-        return Book::class === $to && $data instanceof BookInput;
+        // in the case of an input, the value given here is an array (the JSON decoded).
+        // if it's a book we transformed the data already
+        if ($data instanceof Book) {
+          return false;
+        }
+
+        return Book::class === $to && null !== ($context['input']['class'] ?? null);
     }
 }
 ```
@@ -205,7 +211,11 @@ final class BookInputDataTransformer implements DataTransformerInterface
      */
     public function supportsTransformation($data, string $to, array $context = []): bool
     {
-        return Book::class === $to && $data instanceof BookInput;
+        if ($data instanceof Book) {
+          return false;
+        }
+
+        return Book::class === $to && null !== ($context['input']['class'] ?? null);
     }
 }
 ```