DEFCLASS supports the :METACLASS option. Possible values are STANDARD-CLASS (the default), STRUCTURE-CLASS (which creates structure classes, like DEFSTRUCT does), and user-defined meta-classes (see Section 29.3.6.7, “Generic Function CLOS:VALIDATE-SUPERCLASS”).

It is not required that the superclasses of a class are defined before the DEFCLASS form for the class is evaluated. Use Meta-Object Protocol generic functions CLOS:CLASS-FINALIZED-P to check whether the class has been finalized and thus its instances can be created, and CLOS:FINALIZE-INHERITANCE to force class finalization.

See also Section 29.3.1, “Macro DEFCLASS”.