The Exception __toString implementation will also include the string representation of previous exceptions chained to this exception, _before_ the string representation of the current exception.For example:<?phpclass OuterException extends Exception {}class MiddleException extends Exception {}class InnerException extends Exception {}$excA = new InnerException("inner exception", 0);$excB = new MiddleException("middle exception", 0, $excA);$excC = new OuterException("outer exception", 0, $excB);echo "The exception is:\n$excC";?>will print the following:The exception is:InnerException: inner exception in test.php:6Stack trace:#0 {main}Next MiddleException: middle exception in test.php:7Stack trace:#0 {main}Next OuterException: outer exception in test.php:8Stack trace:#0 {main}