c:\@Work\Perl\monks>perl -wMstrict -le
"print qq{'$1'} if 'ab-cd' =~ m{ (?! \A)    (\w) }xms;
 print qq{'$1'} if 'ab-cd' =~ m{         \b (\w) }xms;
 print qq{'$1'} if 'ab-cd' =~ m{ (?! \A) \b (\w) }xms;
 print qq{'$1'} if 'ab-cd' =~ m{ \b (?! \A) (\w) }xms;
"
'b'
'a'
'c'
'c'

##</code><code>##

c:\@Work\Perl\monks>perl -wMstrict -le
"use Test::More 'no_plan';
 use Test::NoWarnings;
 ;;
 my @regexes = (
   'negative look-ahead to \A',
   qr{ (?! \A) \b (\w) }xms,        qr{ \b (?! \A) (\w) }xms,
   qr{ (?! \A) (?!  \B) (\w) }xms,  qr{ (?!  \B) (?! \A) (\w) }xms,
   qr{ (?! \A) (?<! \B) (\w) }xms,  qr{ (?<! \B) (?! \A) (\w) }xms,
   'negative look-behind to \A',
   qr{ (?<! \A) \b (\w) }xms,        qr{ \b (?<! \A) (\w) }xms,
   qr{ (?<! \A) (?!  \B) (\w) }xms,  qr{ (?!  \B) (?<! \A) (\w) }xms,
   qr{ (?<! \A) (?<! \B) (\w) }xms,  qr{ (?<! \B) (?<! \A) (\w) }xms,
   'all together now',
   qr{ \b (?! \A) (?! \B) (?<! \A) (?<! \B) (\w) }xms,
   );
 ;;
 REGEX:
 for my $rx (@regexes) {
   if (ref $rx ne 'Regexp') {
     note $rx;
     next REGEX;
     }
   'ab-cd' =~ $rx;
   ok $1 eq 'c', qq{$rx works};
   }
 ;;
 done_testing;
"
# negative look-ahead to \A
ok 1 - (?msx-i: (?! \A) \b (\w) ) works
ok 2 - (?msx-i: \b (?! \A) (\w) ) works
ok 3 - (?msx-i: (?! \A) (?!  \B) (\w) ) works
ok 4 - (?msx-i: (?!  \B) (?! \A) (\w) ) works
ok 5 - (?msx-i: (?! \A) (?<! \B) (\w) ) works
ok 6 - (?msx-i: (?<! \B) (?! \A) (\w) ) works
# negative look-behind to \A
ok 7 - (?msx-i: (?<! \A) \b (\w) ) works
ok 8 - (?msx-i: \b (?<! \A) (\w) ) works
ok 9 - (?msx-i: (?<! \A) (?!  \B) (\w) ) works
ok 10 - (?msx-i: (?!  \B) (?<! \A) (\w) ) works
ok 11 - (?msx-i: (?<! \A) (?<! \B) (\w) ) works
ok 12 - (?msx-i: (?<! \B) (?<! \A) (\w) ) works
# all together now
ok 13 - (?msx-i: \b (?! \A) (?! \B) (?<! \A) (?<! \B) (\w) ) works
1..13
ok 14 - no warnings
1..14