[class.compare.default] p6 states that:

The direct base class subobjects of C, in the order of their declaration in the base-specifier-list of C, followed by the non-static data members of C, in the order of their declaration in the member-specification of C, form a list of subobjects.

Presumably, C is inferred to denote a class type from the context of this sentence. However, a "subobject" is defined for the relationship between two objects. It does not make sense to say the subobject of a type.

The improvement may be that:

The direct base class subobjects of an object x of class type C, in the order of their types specified in the base-specifier-list of C, followed by the direct non-static data member subobjects of x, in the order of their declaration in the member-specification of C, form a list of subobjects for x.