7 Expressions [expr]

7.5 Primary expressions [expr.prim]

7.5.4 Names [expr.prim.id] Qualified names [expr.prim.id.qual]

The component names of a qualified-id are those of its nested-name-specifier and unqualified-id.
The component names of a nested-name-specifier are its identifier (if any) and those of its type-name, namespace-name, simple-template-id, and/or nested-name-specifier.
A declarative nested-name-specifier shall not have a decltype-specifier.
A declaration that uses a declarative nested-name-specifier shall be a friend declaration or inhabit a scope that contains the entity being redeclared or specialized.
The nested-name-specifier ​::​ nominates the global namespace.
A nested-name-specifier with a decltype-specifier nominates the type denoted by the decltype-specifier, which shall be a class or enumeration type.
If a nested-name-specifier N is declarative and has a simple-template-id with a template argument list A that involves a template parameter, let T be the template nominated by N without A.
T shall be a class template.
Any other nested-name-specifier nominates the entity denoted by its type-name, namespace-name, identifier, or simple-template-id.
If the nested-name-specifier is not declarative, the entity shall not be a template.
A qualified-id shall not be of the form nested-name-specifier template ~ decltype-specifier nor of the form decltype-specifier ​::​ ~ type-name.
The result of a qualified-id is the entity it denotes ([basic.lookup.qual]).
The type of the expression is the type of the result.
The result is an lvalue if the member is a function, a variable, a structured binding ([dcl.struct.bind]), a static member function, or a data member, and a prvalue otherwise.