It's a slick regex, but you should be aware there's a problem running it with warnings:

#!/usr/bin/perl
                                                                      
+          
use strict;
use warnings;
                                                                      
+          
my $str = "this is abc and bcf and xyz and ijklmn";
                                                                      
+          
while ($str =~ m{
  (                                          # capture to $1
    .                                        # any character
    (?:                                      # this chunk:
      $                                        # either the end of the
+ string
      | (??{ chr(1 + ord substr($&, -1)) })    # or the next character
+ (ASCII-wise) after
                                               # the one we just match
+ed
    )+                                       # one or more times
  )                                          # end capture
}xgs) {
  print "run: <$1>\n";
}
[download]

Produces:

(?:                                      # this chunk:
      $                                        # either the end of the
+ string
      | (??{ chr(1 + ord substr($&, -1)) })    # or the next character
+ (ASCII-wise) after
                                               # the one we just match
+ed
    )+                                       # one or more times
   matches null string many times in regex; marked by <-- HERE in m/
  (                                          # capture to $1
    .                                        # any character
    (?:                                      # this chunk:
      $                                        # either the end of the
+ string
      | (??{ chr(1 + ord substr($&, -1)) })    # or the next character
+ (ASCII-wise) after
                                               # the one we just match
+ed
    )+                                       # one or more times
   <-- HERE )                                          # end capture
/ at ./x line 17.
run: <hi>
run: <abc>
run: <bc>
run: <xyz>
run: <ijklmn>
[download]

Yeah, I know, I got it too. A pox on it.

---

Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart