The whole library (including its modular namespaces) is placed in the Cgu namespace. However, if the --with-cgu-using-directive configuration option is passed to ./configure, each of the library headers has a 'using namespace Cgu' using directive included within it in order to maintain source compatibility for code written against previous versions of the library prior to version 1.2.0.

Because this library uses modular namespaces where relevant, it will usually be perfectly safe to include a 'using namespace Cgu' directive, either via the configuration option mentioned above, or in the user program.