docs: Add clarification on default dialect

Author: DannyvdSluijs

src/JsonSchema/Constraints/Factory.php

@@ -51,7 +51,10 @@ class Factory
      */
     protected $errorContext = Validator::ERROR_DOCUMENT_VALIDATION;
 
-    /** @var string */
+    /**
+     * The default dialect used for strict mode (Constraint::CHECK_MODE_STRICT) when the schema is without a schema property
+     * @var string
+     */
     private $defaultDialect = DraftIdentifiers::DRAFT_6;
 
     /**