         11: [.MajorSeventh, .DiminishedUnison],
     ]
     
+    // MARK: - Interval Families
+    
+    /// Unison interval family.
     public class Unison: EnumFamily {
+        
+        /// Diminished Unison interval.
         public static let Diminished: EnumKind = .DiminishedUnison
+        
+        /// Perfect Unison interval.
         public static let Perfect: EnumKind = .PerfectUnison
+        
+        /// Augmented Unison interval.
         public static let Augmented: EnumKind = .AugmentedUnison
         
         public override class var members: [EnumKind] { return [Perfect, Augmented] }

        }
    }
    
    public class Sixth: EnumFamily {
        public static let Diminished: EnumKind = .DiminishedSixth
        public static let Minor: EnumKind = .MinorSixth
        public static let Major: EnumKind = .MajorSixth
        public static let Augmented: EnumKind = .AugmentedSixth
        
        public override class var members: [EnumKind] {
            return [Diminished, Minor, Major, Augmented]
        }
        
        
        public override class func kind(
            coarseAdjustmentLower: PitchSpelling.CoarseAdjustment,


/// Quality of Interval between two `SpelledPitch` objects.
public class IntervalQuality: EnumTree {

    // MARK: - Associated Types

    public typealias EnumKind = IntervalQualityKind
    public typealias EnumFamily = IntervalQuality
    
