changing the default value of forbidUnknownValues causes errors to be thrown where previously there would not be. I understand its a matter of passing in the options but this still constitutes a breaking change and i think should be reflected in the sem-ver. An application should not completely break when upgrading from x.x.1 to x.x.2. I would prefer that the behavior stay the same but if that is not desired then at least provide a way to set the default globally.