Role composition can be thought of as much more clever and meaningful multiple
inheritance. The basics of this implementation of roles is:
- If a method is already defined on a class, that method will not be composed in
  from the role.
- If a method that the role "requires" to be implemented is not implemented,
  role application will fail loudly.

Unlike Class::C3, where the last class inherited from "wins," role composition
is the other way around, where first wins. In a more complete system (see Moose)
roles are checked to see if they clash. The goal of this is to be much simpler,
hence disallowing composition of multiple roles at once.

WWW: https://metacpan.org/release/Role-Tiny