1  Regexp: a|b(d|e(g|h|i)|f)|c
 2  a: Ok
 3  c: Ok
 4  bd: Ok
 5  bf: Ok
 6  beg: Ok
 7  beh: Ok
 8  bei: Ok
 9  b: Fail
10  be: Fail
11  bi: Fail
12  f: Fail
13  ab: Fail
14  ac: Fail