Are the statutory terms defining nonimmigrant visas in 8 U.S.C. § 1101(a)(15) mere threshold entry requirements that cease to apply once an alien is admitted or do they persist and dictate the terms of a nonimmigrant's stay in the United States?

QUESTION PRESENTED 1. Are the statutory terms defining nonimmigrant visas in 8 U.S.C. § 1101(a)(15) mere threshold entry requirements that cease to apply once an alien is admitted or do they persist and dictate the terms of a nonimmigrant’s stay in the United States? 2. When Congress has enacted a statutory scheme governing a class of aliens in the Immigration and Nationality Act, is the Department of Homeland Security’s power to extend employment authorization to that class of aliens through regulation limited to implementing the terms of that statutory scheme?