andy formless fo _ _123 _abc ab123
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_

// expect: IDENTIFIER andy null
// expect: IDENTIFIER formless null
// expect: IDENTIFIER fo null
// expect: IDENTIFIER _ null
// expect: IDENTIFIER _123 null
// expect: IDENTIFIER _abc null
// expect: IDENTIFIER ab123 null
// expect: IDENTIFIER abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_ null
// expect: EOF  null