“[T]here are several situations in which aliens in the United States have been lawfully admitted, or are pursuing a process for obtaining a lawful status under Federal immigration law, but will not have filed an application or other form that has been designated as complying with registration requirements, and will not have been issued a document designated as evidence of registration. Nonetheless, DHS is aware of their presence through the processes provided by federal immigration law and may, in certain cases, have affirmatively decided not to pursue either removal or criminal prosecution.” June 22, 2010, filed with USA v. Arizona.