Each of the following implements the sheet geometry protocol in a different manner, according to the sheet's requirements.
sheet-identity-transformation-mixin
Summary: This class is mixed into sheet classes whose coordinate systems are identical to that of their parent.
Summary: This class is mixed into sheet classes whose coordinate systems are related to that of their parent by a simple translation.
sheet-y-inverting-transformation-mixin
Summary: This class is mixed into sheet classes whose coordinate systems are related to that of their parent by inverting the y coordinate system, and optionally translating by some amount in x and y .
Summary: This class is mixed into sheet classes whose coordinate systems are related to that of their parent by an arbitrary affine transformation.
Common Lisp Interface Manager 2.0 User's Guide - 7 Aug 2017