1..20
ok 1 - 'abc' -> 'abc'
ok 2 - 'abc.bill.com' -> 'abc'
ok 3 - 'abc.bill.com.au' -> 'abc'
ok 4 - 'xy42.com' -> 'xy42'
ok 5 - 'x_y.com' -> 'x_y'
ok 6 - 'x-y.com' -> 'x-y'
ok 7 - '' -> ''
ok 8 - '.' -> ''
ok 9 - 'a.' -> 'a'
ok 10 - '-.' -> '-'
ok 11 - '_.' -> '_'
ok 12 - '.a' -> ''
ok 13 - 'f' -> 'f'
ok 14 - 'f.1' -> 'f'
ok 15 - 'f.1.2' -> 'f'
ok 16 - 'f.1.2.3' -> 'f'
ok 17 - 'f.1.2.3.4' -> 'f'
ok 18 - 'f.1.2.3.4.5' -> 'f'
ok 19 - 'f.1.2.3.4.5.67' -> 'f'
ok 20 - 'ABC.123.456' -> 'ABC'