To avoid name collisions, HAC supports namespaces. Namespaces are also useful for organizing closely related definitions and instantiations. HAC allows namespaces to be nested, although one-level (flat) namespaces may be emulated by name-mangling.
The default namespace is the global namespace, the ultimate root of all user-defined namespaces. The global namespace has no parent namespace.
See Appendix C.10 (Technicalities:Namespaces) of Stroustrup's The C++ Programming Language.