This appears in the dictionary entry for a class, and contains an ordered list of the classes defined by Common Lisp that must be in the class precedence list of this class.
It is permissible for other (implementation-defined) classes to appear in the implementation’s class precedence list for the class.
It is permissible for either standard-object or structure-object to appear in the implementation’s class precedence list; for details, see Type Relationships.
Except as explicitly indicated otherwise somewhere in this specification, no additional standardized classes may appear in the implementation’s class precedence list.
By definition of the relationship between classes and types, the classes listed in this section are also supertypes of the type denoted by the class.