Clauses [language.support] through [thread] and Annex [depr] do not specify the representation of classes, and intentionally omit specification of class members ([class.mem]). An implementation may define static or non-static class members, or both, as needed to implement the semantics of the member functions specified in Clauses [language.support] through [thread] and Annex [depr].
Objects of certain classes are sometimes required by the external specifications of their classes to store data, apparently in member objects. For the sake of exposition, some subclauses provide representative declarations, and semantic requirements, for private member objects of classes that meet the external specifications of the classes. The declarations for such member objects and the definitions of related member types are followed by a comment that ends with exposition only, as in:
streambuf* sb; // exposition only
An implementation may use any technique that provides equivalent external behavior.