From OpenSCADAWiki
The static class diagram (Fig.4.11.1) does not reveal the entire hierarchy of interaction of the objects, based on the abstract object VCA::Widget. This is due to the implicit inheritance of these properties of the widget across all segments of the engine, as well as with the intricacies of the inheritance, built by using the data of some widgets in the other ones. To explain these features represented the comprehensive map of "using" inheritance in section 4.5.