A class projection provides a way to extend the behavior of the class compiler. The projection mechanism is used by the Java projections; hence the origin of the term projection.
A projection definition instructs the class compiler to perform specified operations when a class definition is compiled or removed. A projection defines the name of a projection class (derived from the %Projection.AbstractProjectionOpens in a new tab class) that implements methods that are called when the compilation of a class is complete and when a class definition is removed (either because it is being deleted or because the class is about to be recompiled).
See Projection Syntax and Keywords in this reference.