(dict-arg-optional) Validation error at line 25 in argument-dict-optional.webidl, inside `interface mixin Container -> operation op1 -> argument shouldBeOptional`:
  undefined op1(Optional shouldBeOptional);
                         ^ Dictionary argument must be optional if it has no required fields
(dict-arg-optional) Validation error at line 31 in argument-dict-optional.webidl, inside `interface mixin Container -> operation op3 -> argument union`:
(Optional or boolean) union);
                      ^ Dictionary argument must be optional if it has no required fields
(dict-arg-optional) Validation error at line 32 in argument-dict-optional.webidl, inside `interface mixin Container -> operation op4 -> argument union`:
  undefined op4(OptionalUnion union);
                              ^ Dictionary argument must be optional if it has no required fields
(dict-arg-optional) Validation error at line 35 in argument-dict-optional.webidl, inside `interface mixin Container -> operation op6 -> argument recursive`:
  undefined op6(Recursive recursive);
                          ^ Dictionary argument must be optional if it has no required fields
(dict-arg-optional) Validation error at line 38 in argument-dict-optional.webidl, inside `interface mixin Container -> operation op8 -> argument lastRequired`:
  undefined op8(Optional lastRequired, optional DOMString yay
                         ^ Dictionary argument must be optional if it has no required fields
(dict-arg-optional) Validation error at line 44 in argument-dict-optional.webidl, inside `interface ContainerInterface -> iterable -> argument shouldBeOptional`:
<DOMString>(Optional shouldBeOptional);
                     ^ Dictionary argument must be optional if it has no required fields