function htmlEncode($html, $in = null, $out = null, $mode = 'auto')
    {
        $valid = array(
            'auto',
            'iconv',
            'mb_convert_encoding'
        );
        if (! isset($out)) {
            $out = 'UTF-8';
        }
        if (! in_array($mode, $valid)) {
            user_error('invalid mode, mode=' . $mode, E_USER_ERROR);
        }
        $if = function_exists('mb_convert_encoding');
        $if = $if && ($mode == 'auto' || $mode == 'mb_convert_encoding');
        $func = null;
        if (function_exists('iconv') && ($mode == 'auto' || $mode == 'iconv')) {
            $func = 'iconv';
        } elseif ($if) {
            $func = 'mb_convert_encoding';
        } else {
            user_error('encode failed, php extension not found', E_USER_ERROR);
        }
        $pattern = '/(<meta[^>]*?charset=(["\']?))([a-z\d_\-]*)(\2[^>]*?>)/is';
        if (! isset($in)) {
            $n = preg_match($pattern, $html, $in);
            if ($n > 0) {
                $in = $in[3];
            } else {
                if (function_exists('mb_detect_encoding')) {
                    $in = mb_detect_encoding($html);
                } else {
                    $in = null;
                }
            }
        }
        if (isset($in)) {
            $old = error_reporting(error_reporting() & ~ E_NOTICE);
            $html = call_user_func($func, $in, $out . '//IGNORE', $html);
            error_reporting($old);
            $html = preg_replace($pattern, "\\1$out\\4", $html, 1);
        } else {
            user_error('source encoding is unknown', E_USER_ERROR);
        }
        return $html;
    }