Davey Shafik cleary explains the new exception hierarchy in PHP 7.

With PHP 7 errors and exceptions are undergoing major changes. For the first time, the PHP engine will start to emit exceptions instead of standard PHP errors for (previously) fatal, and catchable fatal errors. This means that we can now handle them much more gracefully with `try... catch`.

http://daveyshafik.com/archives/69237-an-exceptional-change-in-php-7-0.html