Why Option<_>
Add a comment about why `UnitQuaternion::rotation_between` returns an Option.
@@ -374,7 +374,8 @@ where
}
/// The unit quaternion needed to make `a` and `b` be collinear and point toward the same
- /// direction.
+ /// direction. Returns `None` if both `a` and `b` are collinear and point to opposite directions, as then the
+ /// rotation desired is not unique.
///
/// # Example
/// ```
