Members of an inline namespace can be used in most respects as though they were members
of the innermost enclosing namespace
. Specifically, the inline namespace and its enclosing
namespace are both added to the set of associated namespaces used in
argument-dependent lookup (
[basic.lookup.argdep]) whenever one of them is,
and a
using-directive (
[namespace.udir]) that names the inline
namespace is implicitly inserted into the enclosing namespace as for an unnamed
namespace (
[namespace.unnamed])
. Furthermore, each
member of the inline namespace can subsequently be partially
specialized (
[temp.spec.partial]), explicitly
instantiated (
[temp.explicit]), or explicitly specialized (
[temp.expl.spec]) as
though it were a member of the enclosing namespace
. Finally, looking up a name in the
enclosing namespace via explicit qualification (
[namespace.qual]) will include
members of the inline namespace even if
there are declarations of that name in the enclosing namespace
.