public function compareTo(self $specificity)
    {
        if ($this->a !== $specificity->a) {
            return $this->a > $specificity->a ? 1 : -1;
        }

        if ($this->b !== $specificity->b) {
            return $this->b > $specificity->b ? 1 : -1;
        }

        if ($this->c !== $specificity->c) {
            return $this->c > $specificity->c ? 1 : -1;
        }

        return 0;
    }