[Tex/LaTex] LaTeX strange new environment definition

beamerenvironments

I'm creating a Beamer presentation and I wanted to change margin size for single slides. I've found a solution on some old mailing list, adapted it a little and it works perfectly, but I have no idea how it works=/

\newenvironment{codemargin}{%
  \begin{list}{}{%
        \setlength{\leftmargin}{-0.7cm}%
        \setlength{\rightmargin}{-0.7cm}%
      }%
  \item[]}{
  \end{list}
}

This creates a new environment that I can use on slides that I want to have smaller margins.

Now to the point – what does \item[]}{ mean? I can't find any other examples using similar syntax.

Best Answer

The rough idea is that the list environment (for reasons I don't fully understand) makes various kinds of formatting easier, such as the setlengths you have. I believe it also suppresses the initial paragraph indentation, too. However, just as with the itemize, enumerate, and description environments—which are all wrappers around list—the only permitted text must follow an \item. And since \item can take an optional argument (something used to great effect in description lists), an empty one is provided so that you can write

\begin{codemargin}
  [This text] demonstrates...
\end{codemargin}

Otherwise, the [This text] would get swallowed up by the \item command.

Related Solutions

[Tex/LaTex] Using versions environment tags inside a new environment definition

Don't use \begin{sol} ... \end{sol} in the definition of the Solution environment. \begin ... \end blocks don't nest very well. Rather, use \sol ... \endsol. Thus:

\documentclass{article}
\usepackage{versions}
\excludeversion{sol}
%\includeversion{sol}
\newenvironment{Solution}{
\sol\\ \textbf{Solution: }}{
\endsol}
\begin{document}
\section{Question 1}
What is $2+2$?
\begin{Solution}
It is $2+2=4$.
\end{Solution}
\end{document}

works.

[Tex/LaTex] Environment definition separates matching braces

For applying some macro/command to the body of an environment, you may want to extract the entire body into a macro itself. This can be done (to whatever limited extent) using the environ package. Here is a short example:

\documentclass{article}
\usepackage{environ}% http://ctan.org/pkg/environ
\NewEnviron{itquote}{%
  \itshape% Set shape to italics
  \begin{quote}
    \BODY% regular \BODY of itquote environment
  \end{quote}
}
\begin{document}
\begin{quote}% Original quote environment
  Here is a very simple quote
\end{quote}
\begin{itquote}% New itquote environment
  Here is a very simple quote
\end{itquote}
\end{document}

enter image description here

In the above (admittedly elementary) example, itquote italicizes its contents (stored in the macro \BODY). For some, it provides a more intuitive way of working with environments within environments.

Additionally, it is always good to view the package documentation (and sometimes even the package source .sty). For example, although minipage is an environment and is typically used in the context of \begin{minipage}{<width>} ... \end{minipage} it can also be used in a "macro pair form" using \minipage{<width} ... \endminipage. Again, for some, this allows for a more intuitive way of splitting environment begin/end's over a new environment definition.

Best Answer

Related Solutions

[Tex/LaTex] Using versions environment tags inside a new environment definition

[Tex/LaTex] Environment definition separates matching braces

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