    Instead of em(defining) entities in a namespace, entities may also be
em(declared) in a namespace. This allows us to put all the
    hi(namespace declarations) declarations in a header file that can
thereupon be included in sources using the entities defined in the
namespace. Such a header file could contain, e.g.,
        verb(
    namespace CppAnnotations
    {
        double cos(double degrees);
        double sin(double degrees);
    }
        )
