[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]