If X is a non-union class type, the set M(X) is empty if X has no (possibly inherited (Clause 10)) non-static data members; otherwise, it consists of the type of the first non-static data member of X (where said member may be an anonymous union), X0, and the elements of M(X0).

would be clearer as something like:

If X is a non-union class type with no (possibly inherited (Clause 10)) non-static data members, the set M(X) is empty.
If X is a non-union class type with first non-static data member X0 (where said member may be an anonymous union), the set M(X) consists of X0 and the elements of M(X0).