Describes and discusses the MetaObjectProtocol-extension of the CommonLispObjectSystem (CLOS). It also contains code for a simplified implementation of CLOS and its MetaObjectProtocol. One of the DefinitiveCommonLispBooks.
Chapters four and five contain the detailed specification of the CLOS MOP. They are available as part of the EncyCMUCLopedia from http://www.isr.ist.utl.pt/library/docs/encycmuclopedia/doc/impl/pcl/spec.ps