func strikethroughStyle(_ strikethroughStyle: Int, range: NSRange? = nil) -> NSAttributedString {
        let mutableAttributedString = NSMutableAttributedString(string: string, attributes: attributes())
        mutableAttributedString.addAttribute(NSAttributedString.Key.strikethroughStyle, value: strikethroughStyle, range: attributedStringRange(range))
        return mutableAttributedString as NSAttributedString
    }