The Impact Fund and amici focused on the panel’s misunderstanding of “ascertainability,” a term of art particular to class actions. Ascertainability is the implied prerequisite that a class be defined by clear and definite terms so that a court can determine who is bound by a judgment and who is entitled to relief. Critical to the issue at hand, ascertainability is a forward-looking inquiry, asking whether a court will be able to ascertain class membership at some future point in the litigation. It has never meant that plaintiffs know who is in the proposed class at the time of filing.