Message-Id: <199401071106.AA21327@mail.cs.tu-berlin.de>
Reply-To: Mailing list for the LaTeX3 project <LATEX-L@DHDURZ1.BITNET>
Date:         Thu, 6 Jan 1994 20:13:22 +0100
From: Frank Mittelbach <MITTELBACH@mzdmza.zdv.uni-mainz.de>
Sender: Mailing list for the LaTeX3 project <LATEX-L@DHDURZ1.BITNET>
To: Multiple recipients of list LATEX-L <LATEX-L@DHDURZ1.BITNET>
Subject:      Re: Modification of LaTeX2e distributed files
Status: R

Subj:   RE: Modification of LaTeX2e distributed files

> On Tuesday, January 4 dean.ayres@aea.orgn.uk wrote:
>
> > I maintain style files for producing letters on a variety of letterhead
> > formats.
> > Under LaTeX2.09, each letter style was produced by using a different
> > variation of letter.sty.
> >
> > What is the preferred way of changing the behaviour of LaTeX2e class files
> > such as letter.cls? Should produce edited copies (under a different name, of
> > course, or is there a preferred method?  The changes I want to make are
> > to change \topmargin, \textwidth etc, and to predefine some commands such as
> > \address.
>   I think the best way to do it is to build upon the letter class,
>   especially if you have modifications that are not too large. An
>   example of how to do this can be found in ltxdoc.dtx, the document
>   class that is used in the driver files for the LaTeX2e code.

this concept is supported by \LoadClass \PassOptionsToClass and a few
other commands. You can even built a tree of classes starting with a
generic one and making more special ones on top (that is you can once
we have a slightly better implementation of docclass.dtx in the
official-non-test-release: at the moment too much recursion can give
you stack problems)

by the way, you may notice that the documentation in ltxdoc.dtx might
need improvement, sorry, must have slipped through the fingers
:-). Actually, it is quite possible the this special class will change
a lot during the next weeks.

> > Will a full package writers guide be available in time (or will it be in the
> > companion when available?)
>   It is.

i suppose Johannes meant the Companion. in that case, yes the
Companion contains documentation and examples for this kind of
extensions and the Companion is printed---at least i got a printed
copy from the states just after Christmas. The new addition of
Leslie's book may also contain something about this topic although
this might be too special for a beginners guide. I don't think that we
will provide additional documentation in the distribution in the near
future.

here is an example i use in the companion. It uses the new ifthen
coming with the distribution.

hope that helps a bit

Frank


\begin{verbatim}
% -------------------------------- identification ---------------------------
\NeedsTeXformat{LaTeX2e}
\ProvidesClass{myart}[1994/01/01]
% --------------------------------  initial code ----------------------------
\RequirePackage{ifthen}
\newboolean{cropmarks}
% ---------------------------  declaration of options --
\DeclareOption{cropmarks}{\setboolean{cropmarks}{true}}
\DeclareOption{bind}
    {\AtEndOfClass{\addtolength\oddsidemargin{.5in}%
                   \addtolength\evensidemargin{-.5in}}%
                  }
\DeclareOption*{\PassOptionsToClass{\CurrentOption}{article}}
% ----------------------------  execution of options ------------------------
\ProcessOptions
% --------------------------------package loading ---------------------------
\LoadClass{article}                                  % the real code
% --------------------------------  main code -------------------------------
\newenvironment{Notes}{...}{...}                     % the new environment
\ifthenelse{\boolean{cropmarks}}                     % support for cropmarks
   {%
    \renewcommand{\ps@plain}{....}%
    ....
   }{}
\end{verbatim}