         case .centerX: return .centerX
         case .left: return .left
         case .right: return .right
+        case .leading: return .leading
+        case .trailing: return .trailing
         }
     }
 }

    var nsAttributes: (NSLayoutAttribute, NSLayoutAttribute) {
        switch self {
        case .horizontally: return (.left, .right)
        case .vertically: return (.top, .bottom)
        }
    }

// MARK: Attributes

public enum Horizontal {
    case centerX, left, right, leading, trailing
}

extension Horizontal: SingleOffset, SingleAttribute {
