About ClosedRange's extension and AttributedString

As the code says in ClosedRange+NSRange:

    var nsRange: NSRange { return .init(location: first ?? 0, length: last ?? 0) }

and it's used in AttributedString.swift this function

 @discardableResult
    func addAttribute(_ attr: NSAttributedString.Key, _ value: Any, at range: ClosedRange<Int>? = nil) -> AttributedString {
        // TODO: check range
        let range = range ?? 0..._attributedString.length
        _attributedString.addAttribute(attr, value: value, range: range.nsRange)
        _updateHandler?(_attributedString)
        return self
    }

I'm a bit confuse for how I configured the 'range' such as 23 to 24 because I can't pass 23...24 which means it start at 23 but length is 24 or 23...1 which the first should be smaller or equal the last. I need your help.

Start with ClosedRange+NSRange and the addAttribute function in AttributedString.swift. Reproduce the reported 23...24 case and inspect how the ClosedRange is converted before being passed to NSAttributedString. Done means the intended range behavior is clarified and the conversion or its usage is corrected accordingly.