Secondly: Your posted code does not even compile.

Benchmark: running s///, substr, each for at least 1 CPU seconds...
runloop unable to compile 'my $c = $orig; $c =~ {<!-- TBROWS //-->}{XX
+XX}g;': syntax error at (eval 2) line 1, near "}{XXXX"
syntax error at (eval 2) line 1, near "} }"

code: sub { for (1 .. 1) { local $_; package main; my $c = $orig; $c =
+~ {<!-- TBROWS //-->}{XXXX}g;;} }
 at test_bench.pl line 9
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If you are going to critize, atleast do so in an effective manner.