use strict;

my @testStrs = ("all this<form>", "meh!<form>");

for my $str (@testStrs) {
    my $contents = $str;

    $contents =~ s/^[^<form]*(?=<form)//smg;

    print qq(After: "$contents" Before: "$str"\n);
}

##</code><code>##

After: "<form>" Before: "all this<form>"
After: "meh!<form>" Before: "meh!<form>"

##</code><code>##

use strict;
use warnings;
use HTML::TreeBuilder;

my $htmlFrag = ("<div><form>All good men</form></div>");
my $root = HTML::TreeBuilder->new_from_content($htmlFrag)->elementify();
my $form = $root->look_down("_tag", "form");

print $form->as_text();

##</code><code>##

All good men