enum NSUnderlineStyle : explain the magic

NSUnderlineStyle is an enum where one might expect an option set. In any case, you can see from the abbreviated definition below:

public enum NSUnderlineStyle : Int {
    case StyleNone
    case StyleSingle
    case StyleThick
    case StyleDouble
  
    public static var PatternSolid: NSUnderlineStyle { get }
    case PatternDot
    case PatternDash
    case PatternDashDot
    case PatternDashDotDot
  
    case ByWord
}

What I need are two enum raw values or'd together. It so happened that I am using some functions (String-In-Chain) to build my attributed strings, so I tried something a bit odd to pass a single enum to my function:

let uStyle = NSUnderlineStyle(rawValue: NSUnderlineStyle.PatternDot.rawValue | NSUnderlineStyle.StyleSingle.rawValue)

Amazingly, this worked, but now I'm scratching my head wondering why. Shouldn't I get a nil back? Does this mean Apple has added an extension to the enum to work the magic?

PS: In end end I dropped the above and added a new function to accept an array of enums.