6.3.2.1 Lvalues, arrays, and function designators
1 Anlvalue is an expression with an object type or an incomplete type other than void;53)
if an lvalue does not designate an object when it is evaluated, the behavior is undefined.
When an object is said to have a particular type, the type is specified by the lvalue used to
designate the object. A modifiable lvalue is an lvalue that does not have array type, does
not have an incomplete type, does not have a const-qualified type, and if it is a structure
or union, does not have any member (including, recursively, any member or element of
all contained aggregates or unions) with a const-qualified type.