Davey Shafik has a post today that talks about an exceptional change to PHP 7.0 and some updates that have been made to provide more of a hierarchy (a different one) that can make them easier to work with.
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. But with this change, comes a whole new exception hierarchy.
He provides a tree of the error/exception relationships, what they inherit from and who their "children" are. He also talks more in detail about the "error" type exceptions: Error, AssertionError, ParseError and TypeError. He gets into more detail about catchable fatal errors and the userland handling of the Throwable type and extension.