Habari\InputFilter::_validate_entity PHP Method

    public static function _validate_entity($m)
    {
        $is_valid = false;
        /**
         * valid entity references have the form
         *   /&named([;<\n\r])/
         * for named entities, or
         *   /&#(\d{1,5}|[xX][0-9a-fA-F]{1,4})([;<\n\r])/
         * for numeric character references
         */
        $e = trim($m[1]);
        $r = $m[2];
        if ($r == ';') {
            $r = '';
        }
        if ($e[0] == '#') {
            $e = strtolower($e);
            if ($e[1] == 'x') {
                $e = hexdec(substr($e, 2));
            } else {
                $e = substr($e, 1);
            }
            // numeric character references may only have values in the range 0-65535 (16 bit)
            // we strip null, though, just for kicks
            $is_valid = intval($e) > 8 && intval($e) <= 65535;
            if ($is_valid) {
                // normalize to decimal form
                $e = '#' . intval($e) . ';';
            }
        } else {
            if (self::$character_entities_re == '') {
                self::$character_entities_re = ';(' . implode('|', self::$character_entities) . ');';
            }
            // named entities must be known
            $is_valid = preg_match(self::$character_entities_re, $e, $matches);
            // XXX should we map named entities to their numeric equivalents?
            if ($is_valid) {
                // normalize to name and nothing but the name... eh.
                $e = $matches[1] . ';';
            }
        }
        return $is_valid ? '&' . $e . $r : '';
    }