The article, report and book classes of current LaTeX (and their class option files) all derive from a single source file, classes.dtx; its contents are extracted to the class files themselves in the course of installing LaTeX.
Of course, since classes.dtx is a documented source file, it may be formatted, for (perhaps) more relaxed reading. A formatted version exists in the base and latex-tds zip files of the LaTeX-TDS distribution.
The author is The LaTeX Team. The package is Copyright © 1993-2006 The LaTeX3 Project.
License: lppl Version dated: 2005-12-01 Catalogued: 2015-08-03