Hello guys. Can someone explain to me how would one come up with the idea behind the code from line 12 to 18? I mean I kind of understand it but I would have never though of it :-). (It's from Intermediate Perl book, by the way).

     1  #!perl

     2  use strict;
     3  use warnings;
     4  use utf8;

     5  use File::Find;
     6  use Time::Local;

     7  my $target_dow = 1;        # Sunday is 0, Monday is 1, ...
     8  my @starting_directories = (".");

     9  my $seconds_per_day = 24 * 60 * 60;
    10  my($sec, $min, $hour, $day, $mon, $yr, $dow) = localtime;
    11  my $start = timelocal(0, 0, 0, $day, $mon, $yr);        # midn
+ight today

    12  while ($dow != $target_dow) {
    13    # Back up one day
    14    $start -= $seconds_per_day;        # hope no DST! :-)
    15    if (--$dow < 0) {
    16      $dow += 7;
    17    }
    18  }
    19  my $stop = $start + $seconds_per_day;

    20  my($gather, $yield)  = gather_mtime_between($start, $stop);
    21  find($gather, @starting_directories);
    22  my @files = $yield->(  );

    23  for my $file (@files) {
    24    my $mtime = (stat $file)[9];        # mtime via slice
    25    my $when = localtime $mtime;
    26    print "$when: $file\n";
    27  }
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