The attribute-token maybe_unused indicates that a name or entity is possibly intentionally unused. It shall appear at most once in each attribute-list and no attribute-argument-clause shall be present.
The attribute may be applied to the declaration of a class, a typedef-name, a variable, a non-static data member, a function, an enumeration, or an enumerator.
[ Note: For an entity marked maybe_unused, implementations are encouraged not to emit a warning that the entity is unused, or that the entity is used despite the presence of the attribute. — end note ]
A name or entity declared without the maybe_unused attribute can later be redeclared with the attribute and vice versa. An entity is considered marked after the first declaration that marks it.