use Benchmark qw(cmpthese);
@l = ("A".."Z","a".."z",qw(< / >),0..9);
$x = join( '', map { $l[ rand @l ] } 1 .. 100_000 ) . "</body></html>";

cmpthese ( -1,
  {
    noanchor => sub { local $_ = $x; s|(</body></html>)|zzz$1| },
    anchor   => sub { local $_ = $x; s|(</body></html>)$|zzz$1| },
  }
);
           Rate noanchor   anchor
noanchor 5023/s       --     -19%
anchor   6222/s      24%       --