How to understand and write LaTeX code?

Question

LaTeX is like a language. In order to write LaTeX code I have to understand the "word" and the "sentences structure". I have searched on wiki, some LaTeX books, but they just give the LaTeX command, not how to write a LaTeX code for some specific purpose or to understand the LaTeX code.

Here is one example:

\renewenvironment{svgraybox}%
       {\fboxsep=12pt\relax
        \begin{shaded}%
        \list{}{\leftmargin=12pt\rightmargin=2\leftmargin\leftmargin=\z@\topsep=\z@\relax}%
        \expandafter\item\parindent=\svparindent
        \hskip-\listparindent}%
       {\endlist\end{shaded}}%
%
\renewenvironment{svtintedbox}%
       {\fboxsep=12pt\relax
        \begin{tinted}%
        \list{}{\leftmargin=12pt\rightmargin=2\leftmargin\leftmargin=\z@\topsep=\z@\relax}%
        \expandafter\item\parindent=\svparindent
        \relax}%
       {\endlist\end{tinted}}%
%
}}
%
\let\SVMonoOpt\@empty

I do not know what is \z@, what is \relax, what is \fboxsep ... and if I want to design my LaTeX file in my own form, I know that I have to understand many other things.

Note that I can write simple LaTeX enviroment in mathematics (like the matrix, align, enviroment) but it does not help me to understand the above code.

So, what could I do? What book should I read? Or what programming language should I learn?

Answer 1

The TeXbook is the best place to learn about the underlying TeX language, although TeX-by-Topic (texdoc texbytopic) in most distributions is a good free alternative. But much of what you show is not directly using TeX primitives but using constructs such as \list defined in the latex format. The LaTeX Companion has detail for that or the free documented sources of LaTeX texdoc source2e has lots of information.

This site of course can also be used. For example

• on \z@ What does \z@ do?

• on list parameters, several answers, e.g., How to create a custom list and \item element?

• on \relax for example What is the difference between \relax and {}?

• on \expandafter lots of questions, e.g., When to use \edef, \noexpand, and \expandafter? but note the usage in the code you show is in error, it is harmless but does nothing.

Answer 2

You can find out what any command does by asking LaTeX itself. Just open up a console window and run latex (or whatever variant you prefer), and then you can issue commands line by line.

For example, to find out what \z@ means, you can use

$ latex
**\makeatletter
*\show\z@

and LaTeX will give you

> \z@=\dimen12.

(The \makeatletter command allows you to use the @ sign in commands.)

If you want to find out what length is stored in \dimen12, you can then use

*\showthe\dimen12

which will give you

> 0.0pt

So the \z@ command is a short hand for a zero length.

The \show command will tell you the definition of any command except a primitive; you can look those up online with a Google search.