public function addFilter($filter)
    {
        if (is_string($filter)) {
            $filter = trim($filter);
        } elseif (! $filter instanceof Filter) {
            throw new \UnexpectedValueException('Expceted instanceof Org\Heigl\Hyphenator\Filter\Filter or string');
        }
        if (! $filter) {
            return $this;
        }
        $this->filters[] = $filter;

        return $this;
    }