 /// Protocol to provide values to be used by `UIFontFeatureTypeIdentifierKey` and `UIFontFeatureSelectorIdentifierKey`.
 /// You can typically find these values in CoreText.SFNTLayoutTypes
 public protocol FontFeatureProvider {
-    func featureSettings() -> (Int, Int)
+    func featureSettings() -> (type: Int, selector: Int)
 }
 
 public extension BONFont {

    func featureAttribute() -> StyleAttributes {
        let featureSettings = self.featureSettings()
        return [
            BONFontFeatureTypeIdentifierKey: featureSettings.0,
            BONFontFeatureSelectorIdentifierKey: featureSettings.1
        ]
    }
}

/// An enumeration representing the kNumberSpacingType features.
public enum NumberSpacing: FontFeatureProvider {
    case monospaced, proportional
    public func featureSettings() -> (type: Int, selector: Int) {
        switch self {
        case .monospaced:
            return (type: kNumberSpacingType, selector: kMonospacedNumbersSelector)
        case .proportional:
            return (type: kNumberSpacingType, selector: kProportionalNumbersSelector)
        }
    }
}
