Update validation.md

validation.md

@@ -693,7 +693,7 @@ The field under validation must be equal to the given date. The dates will be pa
 <a name="rule-date-format"></a>
 #### date_format:_format_
 
-The field under validation must match the given _format_. You should use **either** `date` or `date_format` when validating a field, not both. The formats allowed are the ones for [DateTime](https://www.php.net/manual/es/class.datetime.php) class.
+The field under validation must match the given _format_. You should use **either** `date` or `date_format` when validating a field, not both. This validation rule supports all formats supported by PHP's [DateTime](https://www.php.net/manual/es/class.datetime.php) class.
 
 <a name="rule-different"></a>
 #### different:_field_