20 Library introduction [library]

20.3 Definitions [definitions]

20.3.25 valid but unspecified state [defns.valid]

a value of an object that is not specified except that the object's invariants are met and operations on the object behave as specified for its type
[Example: If an object x of type std​::​vector<int> is in a valid but unspecified state, x.empty() can be called unconditionally, and x.front() can be called only if x.empty() returns false. end example]