PR clean-up.

Author: bryanedds

Nu/Nu/Physics/PhysicsEngine.fs

@@ -98,33 +98,43 @@ type [<NoEquality; NoComparison>] BodyUserObject =
      Constants.PrettyPrinter.DefaultThresholdMin,
      Constants.PrettyPrinter.SimpleThresholdMax)>]
 type Substance =
+
     /// Density is calculated from dividing constant mass by volume.
     | Mass of Mass : single
-    /// Mass is calculated from multiplying constant density with volume.
+
+    /// Mass is calculated from multiplying constant density with volume (may be approximate).
     | Density of Density : single
 
 /// Describe the form of collision detection to use.
 type CollisionDetection =
+
     /// Use discrete collision detection.
     /// This is the fastest form of collision detection, but fast-moving objects may tunnel through other
     /// objects without detecting a collision.
     | Discontinuous
+
     /// Use continuous collision detection.
     /// This form of collision detection is slower, but fast-moving objects will not tunnel through other
     /// objects without detecting a collision.
     | Continuous
 
 /// Describes the physical profile of a complex body.
 type Profile =
+
     /// A convex shape.
     /// This shape is defined by a body that forms a convex hull.
+    /// Moderately efficient but accurate enough for many cases.
     | Convex
+
     /// A concave shape.
     /// This shape is defined by a body may form a concave hull.
-    // TODO: Should this case be specified to require points to be formatted as groups of 3 to form triangles even for user defined 2D and 3D engines?
+    /// Least efficient but often more accurate.
+    /// TODO: should this case be specified to require points to be formatted as groups of 3 to form triangles even for user-defined 2D and 3D engines?
     | Concave
+
     /// A simplified axis-aligned bounds.
     /// This shape is defined by a bounding box around a body.
+    /// Most efficient but least accurate.
     | Bounds
 
 /// The shape of a physics body box.