The file GUIbase.h is a bit irritating, because
- it contains a number of unrelated classes and functions, so it's not clear what it's designed purpose is, it's not clear when it should be included (other than requiring one of the types),
- while all other GUI files contain one file per class
- GUIbase.cpp only contains the implementation for CGUISize that is named CClientArea and relates to JSI_GUISize.