Otherwise, the terminal name of the declarator-id is not looked up. If it is a qualified name, the declarator shall correspond to one or more declarations nominable in S; all the declarations shall have the same target scope and the target scope of the declarator is that scope.
[Example 2: 
namespace Q {
  namespace V {
    void f();
  }
  void V::f() { /* ... */ }     // OK
  void V::g() { /* ... */ }     // error: g() is not yet a member of V
  namespace V {
    void g();
  }
}
namespace R {
  void Q::V::g() { /* ... */ }  // error: R doesn't enclose Q
}
— end example]

Members of a named namespace can also be defined outside that namespace by explicit qualification ([namespace.qual]) of the name being defined, provided that the entity being defined was already declared in the namespace and the definition appears after the point of declaration in a namespace that encloses the declaration's namespace.