Chapter 9

Sealing

# 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`.