Win8 Strawberry 5.8.9.5 (32)  Tue 12/22/2020 16:43:09
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings
for my $line (
    '<div id="foo-bar-321" class="bin-boff"></div>',
    '<div id="foo-bar-321" class="bin-boff"> </div>',
    '<div id="foo-bar-321" class="bin-boff">foo</div>',
    '<div id="foo-bar-321" class="bin-boff"> foo </div>',
    '<div id="foo-bar-321" class="bin-boff">',
    '<div id="foo-bar-321" class="bin-boff">  ',
    '<div id="foo-bar-321" class="bin-boff">foo',
    '<div id="foo-bar-321" class="bin-boff"> foo',
    ) {

    if ($line =~ m{ <div (?: (?! </div) .)+ (</div)? }xms) {
        print "line matched \n  '$&' \n";
        if (defined $1) {
            print "  right after match, \$1 is defined '$1' \n";
            }
        }

    }
^Z
line matched
  '<div id="foo-bar-321" class="bin-boff"></div'
  right after match, $1 is defined '</div'
line matched
  '<div id="foo-bar-321" class="bin-boff"> </div'
  right after match, $1 is defined '</div'
line matched
  '<div id="foo-bar-321" class="bin-boff">foo</div'
  right after match, $1 is defined '</div'
line matched
  '<div id="foo-bar-321" class="bin-boff"> foo </div'
  right after match, $1 is defined '</div'
line matched
  '<div id="foo-bar-321" class="bin-boff">'
line matched
  '<div id="foo-bar-321" class="bin-boff">  '
line matched
  '<div id="foo-bar-321" class="bin-boff">foo'
line matched
  '<div id="foo-bar-321" class="bin-boff"> foo'