sub _is_html_clean {
    # create state variable contain hash of unbalanced tags
    # that will persist across calls
    state $is_unbalanced = {
        area       => 1,
        base       => 1,
        basefont   => 1,
        bgsound    => 1,
        br         => 1,
        col        => 1,
        colgroup   => 1,
        embed      => 1,
        frame      => 1,
        hr         => 1,
        img        => 1,
        input      => 1,
        isindex    => 1,
        li         => 1,
        link       => 1,
        marquee    => 1,
        meta       => 1,
        p          => 1,
        '!doctype' => 1,
    };

    # remove self closing tags
    $_[0] =~ s/(.*)<.+?\/>/$1/g;

    # remove commented sections
    $_[0] =~ s/<!--.+?-->//msg;

    # load tag names in array
    my (@a) = ( $_[0] =~ m/<(\S+?)[ >]/msg );

    # process each tag counting the open and closes and
    # then increment or decrement a counter for that tag
    my %h;
    foreach (@a) {
        if (m[^/]) {     # closing tag
            substr( $_, 0, 1 ) = "";     # remove the /
            $h{$_}--;
        }
        else {
            $h{$_}++;
        }
    }

    foreach ( keys %h ) {
        if (m/[A-Z]/) {
            # combine keys in case insensitive manner
            $h{ lc($_) } += $h{$_};
            delete $h{$_};
        }
    }

    foreach ( sort keys %h ) {
        next if ( $is_unbalanced->{$_} ); # ignore if tag is in the is unbalanced hash
        if ( $h{$_} != 0 ) {
            return 0;     # return as soon as an non-paired tag is found
        }
    }

    return 1;     # return if all is good
}