Explicitly Known Objects

A class, generic function, or method may or may not be explicitly known to a given library. A sealing restriction may limit the set of classes, generic functions, and methods to those that are explicitly known; others cannot be added.

A class C is explicitly known in a library L if it is defined by define class in L or in a library used by L.
A generic function G is explicitly known in a library L if G is defined by define generic in the library or in one of the libraries L uses, or if G is implicitly defined by the definition of a method explicitly known in L or if G is implicitly defined by a slot specification for a class explicitly known in L.
A method M is explicitly known in a library L if M is defined by define method in L or in one of the libraries L uses, or if M is defined by a slot specification for a class explicitly known in L.