public function brace($m)
    {
        if ($m[0] === '{') {
            $this->braceStack++;
        } elseif ($m[0] === '}') {
            if ($this->braceStack <= 0) {
                return true;
            }
            $this->braceStack--;
        } else {
            assert(0);
        }
        $this->record($m[0], null);
        $this->posShift(strlen($m[0]));
    }