This diagram represents "contains" type of the relation between 2 classes, i.e. when an instance of the class holds some of instances of the other classes and expose access to them through certain properties. For example an instance of Shapefile class may hold several instance of Shape class (1 to 0..n relation), an instance of Shape class in the same manner may hold points.
The diagrams are interactive. After the click on the rectangle the description of corresponding class will be shown, after the click on the arrow - a property which extracts instances of nested class. These diagrams has nothing to do with the inheritance.
The description of some large classes is separated into several pages, which are called modules. This type of diagram is used for faster navigation between such groups. In case the methods and properties of the module were deprecated the gray color will be used.
1.9.3