>perl -wMstrict -le
"use Test::More 'no_plan';
 use Test::NoWarnings;
 ;;
 my @vectors = (
   [ 'chapters 01,02,03,04',              qw(01 02 03 04), ],
   [ 'chapters 1 , 2 , 3 , 4 , 5',        qw(1 2 3 4 5),   ],
   [ 'in chapter 01',                     qw(01),          ],
   [ 'chapter 101',                       qw(101),         ],
   [ 'chapters 99, 100 ,101 also',        qw(99 100 101),  ],
   [ 'chapters 3, 4, 5 and chapter 9',    qw(3 4 5 9),     ],
   [ 'read chapters 3, 4 and chapter 9',  qw(3 4 9),       ],
   'pay particular attention to the next variation',
   [ 'chapters 3, 4, 5 and 9',            qw(3 4 5),       ],
   'no chapter numbers should be extracted from any of these',
   [ 'chapter' ], [ 'chapters' ], [ 'chapter ii' ], [ '01,02' ],
   );
 ;;
 VECTOR:
 for my $ar_vector (@vectors) {
   unless (ref $ar_vector) {
     note $ar_vector;
     next VECTOR;
     }
   my ($s, @expected) = @$ar_vector;
   my @n = $s =~ m{
     (?: \G (?<! \A) \s* , \s* | chapters? \s+) \K
     \d+
     }xmsg;
   is_deeply \@n, \@expected, qq{'$s' -> (@expected)};
   }
"
ok 1 - 'chapters 01,02,03,04' -> (01 02 03 04)
ok 2 - 'chapters 1 , 2 , 3 , 4 , 5' -> (1 2 3 4 5)
ok 3 - 'in chapter 01' -> (01)
ok 4 - 'chapter 101' -> (101)
ok 5 - 'chapters 99, 100 ,101 also' -> (99 100 101)
ok 6 - 'chapters 3, 4, 5 and chapter 9' -> (3 4 5 9)
ok 7 - 'read chapters 3, 4 and chapter 9' -> (3 4 9)
# pay particular attention to the next variation
ok 8 - 'chapters 3, 4, 5 and 9' -> (3 4 5)
# no chapter numbers should be extracted from any of these
ok 9 - 'chapter' -> ()
ok 10 - 'chapters' -> ()
ok 11 - 'chapter ii' -> ()
ok 12 - '01,02' -> ()
ok 13 - no warnings
1..13