foreach ($member_sheet -> contents =~ /(\<.*?\/?\>|.*?(?=\<))/g) {
 ...

##</code><code>##

my $buffer = $member_sheet -> contents();
#while ($buffer =~ /\G(<[^<]*>)/scg or $buffer =~ /\G([^<]*(?=<))/scg) {
while ($buffer =~ /(<[^>]+>|[^<]+(?=<))/sg) {
    $_ = $1;
...

##</code><code>##

use Benchmark qw(cmpthese);

open(my $fh, "<", 'sheet3.xml') or die "Err: $!";
my $str = do { local $/; <$fh>};

cmpthese(-10, {

  FOR   => sub {
    pos($str) = 0;
    for ( $str =~ /(\<.*?\/?\>|.*?(?=\<))/g ) {
      #print "$_\n";
    }
  },
  WHILE_1 => sub {
    pos($str) = 0;
    while ( $str =~ /\G(<.*?>|.*?(?=<))/scg ) {
      $_ = $1;
      #print "$_\n";
    }
  },
  WHILE_2 => sub {
    pos($str) = 0;
    while ( $str =~ /\G(<.*?>)/scg or $str =~ /\G(.*?(?=<))/scg ) {
      $_ = $1;
      #print "$_\n";
    }
  },
  WHILE_3 => sub {
    pos($str) = 0;
    while ( $str =~ /\G(<[^>]*>)/scg or $str =~ /\G([^<]*(?=<))/scg ) {
      $_ = $1;
      #print "$_\n";
    }
  },
});

# Results:
        s/iter     FOR WHILE_3 WHILE_2 WHILE_1
FOR       1.66      --    -27%    -31%    -35%
WHILE_3   1.21     37%      --     -6%    -11%
WHILE_2   1.14     46%      6%      --     -5%
WHILE_1   1.08     53%     12%      5%      --