Exception::class allows you to declare exceptions in your modules in a manner similar to how exceptions are declared in java.

it features a simple interface allowing programmers to 'declare' exception classes at compile time. it also has a base exception class, exception::class::base, that can be used for classes stored in files (aka modules ;) ) that are subclasses.

it is designed to make structured exception handling simpler and better by encouraging people to use hierarchies of exceptions in their applications.