We discuss a general method for classifying certain subcategories of the category of
finite-dimensional modules over a finite-dimensional co-commutative Hopf algebra
B. Our method is based on that of Benson–Carlson–Rickard [BCR1], who classify
such subcategories when B = kG, the group ring of a finite group G over an algebraically
closed field k. We get a similar classification when B is a finite sub-Hopf algebra
of the mod 2 Steenrod algebra, with scalars extended to the algebraic closure of F2.
Along the way, we prove a Quillen stratification theorem for cohomological varieties
of modules over any B, in terms of quasi-elementary sub-Hopf algebras of B.