I could be wrong, but that is how I interpreted this section.
"default-default" and "default-abstract" are not keywords. They describe two different compilation conflict rules related to default methods in an interface.
"default-default", referring to a class that implements two or more interfaces that provide standard implementations of overriding equivalent methods without providing them with their own implementation.
"default-abstract", referring to a class that implements one interface that provides a default implementation, and one or more interfaces that do not provide standard implementations of overriding equivalent methods.
The exception to these two rules is if the superclass of the class in question defines an abstract method that overrides the equivalent that intercepts the definitions found in any implementation interface.
If a class inherits a specific overriding equivalent method from a superclass or defines its own, then none of these conflicts apply.