:meth:`.WCommandProto.exec` implementation

def exec(self, *command_tokens, **command_env):
		""" :meth:`.WCommandProto.exec` implementation
		"""
		mutated_command_tokens = self.mutate_command_tokens(*command_tokens)
		if mutated_command_tokens is not None:
			command = self.selector().select(*mutated_command_tokens, **command_env)
			if command is not None:
				return command.exec(*mutated_command_tokens, **command_env)

		raise RuntimeError('Command mismatch: %s' % self.join_tokens(*command_tokens))