In general, an implementation is free to ignore declaration specifiers except for the declaration, notinline, safety, and special declaration specifiers.
A declaration declaration must suppress warnings about unrecognized declarations of the kind that it declares. If an implementation does not produce warnings about unrecognized declarations, it may safely ignore this declaration.
A notinline declaration must be recognized by any implementation that supports inline functions or compiler macros in order to disable those facilities. An implementation that does not use inline functions or compiler macros may safely ignore this declaration.
A safety declaration that increases the current safety level must always be recognized. An implementation that always processes code as if safety were high may safely ignore this declaration.
A special declaration must be processed by all implementations.