Here is the new class comments I'm trying to write. I hope that it will help people to understand the circumstances under which they should use fractions:offset: creation API. I define a transformation frame relative to some rectangle. I'm basic data structure used for graphics. I represent two groups of distances: - The fractional distance (between 0 and 1) to place the morph in its owner's bounds - Fixed pixel offset to apply after fractional positioning (e.g., "10 pixel right of the center of the owner") !! API usage It is important to understand that it is better to use the fine grained API using elementary distances (bottomFraction:, bottomOffset:, leftFraction: ....) than the ones (historical) using points and rectangles (fractions:offsets:) The reason is that the old API (fractions:offsets:) is only interesting if you already have a rectangle and points at hand. If you need to create new ones, then they are created for nothing because they will be destructured to extract their information to be feed into the layoutFrame. So please do not blindly copy and paste code! Example: Favor (LayoutFrame identity leftFraction: 0; yourself); (LayoutFrame identity leftFraction: 0.5; rightFraction: 0.95; (LayoutFrame identity topOffset: topHeight; bottomFraction: 0; bottomOffset: self buttonsBarHeight; leftOffset: -1; rightOffset: 1) over (LayoutFrame fractions: (0 @ 0 corner: 1 @ 1)) because you are creating for nothing a new rectangle and some points. !! Implementation Instance variables: The fractional distance (between 0 and 1) to place the morph in its owner's bounds is represented by the following instance variables: leftFraction topFraction rightFraction bottomFraction <Float> Fixed pixel offset to apply after fractional positioning (e.g., "10 pixel right of the center of the owner") is represented by the following instance variables: leftOffset topOffset rightOffset bottomOffset <Integer>