$ perl -Mre=debug -e'"aaaaaaaaaaaaaaa" =~ /^a+[bB]/'
...
Matching REx "^a+[bB]" against "aaaaaaaaaaaaaaa"
   0 <> <aaaaaaaaaa>         |  1:BOL(2)
   0 <> <aaaaaaaaaa>         |  2:PLUS(5)
                                  EXACT <a> can match 15 times out of 2147483647...
  15 <aaaaaaaaaaaa> <>       |  5:  ANYOF[Bb][](16)
                                    failed...
  14 <aaaaaaaaaaa> <a>       |  5:  ANYOF[Bb][](16)
                                    failed...
  13 <aaaaaaaaaa> <aa>       |  5:  ANYOF[Bb][](16)
                                    failed...
  12 <aaaaaaaaa> <aaa>       |  5:  ANYOF[Bb][](16)
                                    failed...
  11 <aaaaaaaa> <aaaa>       |  5:  ANYOF[Bb][](16)
                                    failed...
  10 <aaaaaaa> <aaaaa>       |  5:  ANYOF[Bb][](16)
                                    failed...
   9 <aaaaaa> <aaaaaa>       |  5:  ANYOF[Bb][](16)
                                    failed...
   8 <aaaaa> <aaaaaaa>       |  5:  ANYOF[Bb][](16)
                                    failed...
   7 <aaaaa> <aaaaaaaa>      |  5:  ANYOF[Bb][](16)
                                    failed...
   6 <aaaaa> <aaaaaaaaa>     |  5:  ANYOF[Bb][](16)
                                    failed...
   5 <aaaaa> <aaaaaaaaaa>    |  5:  ANYOF[Bb][](16)
                                    failed...
   4 <aaaa> <aaaaaaaaaa>     |  5:  ANYOF[Bb][](16)
                                    failed...
   3 <aaa> <aaaaaaaaaa>      |  5:  ANYOF[Bb][](16)
                                    failed...
   2 <aa> <aaaaaaaaaa>       |  5:  ANYOF[Bb][](16)
                                    failed...
   1 <a> <aaaaaaaaaa>        |  5:  ANYOF[Bb][](16)
                                    failed...
                                  failed...
Match failed
...

$ perl -Mre=debug -e'"aaaaaaaaaaaaaaa" =~ /^a++[bB]/'
...
Matching REx "^a++[bB]" against "aaaaaaaaaaaaaaa"
   0 <> <aaaaaaaaaa>         |  1:BOL(2)
   0 <> <aaaaaaaaaa>         |  2:SUSPEND(9)
   0 <> <aaaaaaaaaa>         |  4:  PLUS(7)
                                    EXACT <a> can match 15 times out of 2147483647...
  15 <aaaaaaaaaaaa> <>       |  7:    SUCCEED(0)
                                      subpattern success...
  15 <aaaaaaaaaaaa> <>       |  9:ANYOF[Bb][](20)
                                  failed...
Match failed
...