Inheritance offers a straightforward way to easily spawn a large number of objects that are semantically related to each other without having duplicate code. The concept is ridiculously simple - yet powerful: you first drop as much logic as possible within the boundaries of a base type (usually an abstract class, but it could be a concrete one), and then start deriving refined subtypes according to more specific requirements. [...] Not surprisingly, this repetitive encapsulation/derivation cycle lays down on the formalities of a design pattern known as Layer Supertype.

They describe the "supertype" as a replacement for an overly bloated domain-related model. Their example replaces a PostInterface/CommentInterface with a more generic "AbstractEntity" that handles some of the basics for you - getting/setting, checking a field, setting an ID and outputing the information to an array.