16.4 Namespace members

A namespace-member-declaration is either a namespace-declaration (§16.2) or
a type-declaration (§16.5).
namespace-member-declarations:
namespace-member-declaration
namespace-member-declarations namespace-member-declaration
namespace-member-declaration:
namespace-declaration
type-declaration
A compilation unit or a namespace body can contain
namespace-member-declarations, and such
declarations contribute new members to the underlying declaration space of
the containing compilation unit
or namespace body.