6 Basics [basic]

6.4 Scope [basic.scope]

6.4.6 Namespace scope [basic.scope.namespace]

Any namespace-definition for a namespace N introduces a namespace scope that includes the namespace-body for every namespace-definition for N.
For each non-friend redeclaration or specialization whose target scope is or is contained by the scope, the portion after the declarator-id, class-head-name, or enum-head-name is also included in the scope.
The global scope is the namespace scope of the global namespace ([basic.namespace]).
[Example 1: namespace Q { namespace V { void f(); } void V::f() { // in the scope of V void h(); // declares Q​::​V​::​h } } — end example]