...
Guessed: match at offset 0
   2 <a%n> <%n%nb>           |  1:MBOL(2)
   2 <a%n> <%n%nb>           |  2:MINMOD(3)
   2 <a%n> <%n%nb>           |  3:STAR(5)
   2 <a%n> <%n%nb>           |  5:  MEOL(6)
   2 <a%n> <%n%nb>           |  6:  END(0)
Match possible, but length=0 is smaller than requested=1, failing!
                                  POSIXD[\s] can match 1 times out of 1...
   3 <a%n%n> <%nb>           |  5:  MEOL(6)
   3 <a%n%n> <%nb>           |  6:  END(0)
Match successful!
...