Fixes #1514: added more doc.

framework/yii/validators/UrlValidator.php

@@ -16,6 +16,9 @@ use yii\helpers\Json;
 /**
  * UrlValidator validates that the attribute value is a valid http or https URL.
  *
+ * Note that this validator only checks if the URL scheme and host part are correct.
+ * It does not check the rest part of a URL.
+ *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */