    public function validate($number, $config, $context) {

        $number = $this->parseCDATA($number);

        if ($number === '') return false;
        if ($number === '0') return '0';

        $sign = '';
        switch ($number[0]) {
            case '-':
                if ($this->non_negative) return false;
                $sign = '-';
            case '+':
                $number = substr($number, 1);
        }

        if (ctype_digit($number)) {
            $number = ltrim($number, '0');
            return $number ? $sign . $number : '0';
        }

        // Period is the only non-numeric character allowed
        if (strpos($number, '.') === false) return false;

        list($left, $right) = explode('.', $number, 2);

        if ($left === '' && $right === '') return false;
        if ($left !== '' && !ctype_digit($left)) return false;

        $left  = ltrim($left,  '0');
        $right = rtrim($right, '0');

        if ($right === '') {
            return $left ? $sign . $left : '0';
        } elseif (!ctype_digit($right)) {
            return false;
        }

        return $sign . $left . '.' . $right;

    }
The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.