The texdoc command described earlier is not restricted to package sources. If you wish to
go beyond the areas covered by this course and study the LaTeX inplementation in detail then
the following links may help.
The source of LaTeX itself is available as a LaTeX-typeset document source2e.pdf, available at
texdoc.net
Current releases of LaTeX also have preloaded the LaTeX3 Programming Language code, previously available
as the expl3 package. texdoc may be used to see the
expl3 interface description
or
full expl3 source code.