Lesson 6

The \usepackage command takes a comma-separated list of packages, so you can load several in one go: \usepackage{color,graphicx} for example. If you are passing options to a package, they will apply to each of the packages in the list. It’s also easier to comment out packages if they are loaded separately. So we will stick to loading each package on a separate line.

## The babel package

We showed the babel package in the main lesson as a way to choose different hyphenation patterns. It does a lot more than that, depending on the language(s) being used. For example, in German, it provides some shorthands for creating ‘soft’ hyphens, and also a way to quickly type umlauts without needing a German keyboard. Note also how the section heading Table of Contents normally generated by \tableofcontents is changed to the German Inhaltsverzeichnis.

\documentclass{article}
\usepackage[T1]{fontenc}

\usepackage[ngerman]{babel} % Notice that the option name is 'ngerman'

\begin{document}

\tableofcontents

\section{"Uber "Apfel und Birnen}

\subsection{Äpfel}
Äpfel sind rot.

\subsection{Birnen}
Birnen sind gelb.

\end{document}


Other language settings make design changes: for example, in traditional French typography, there is a space before some punctuation signs, like :, and this is added automatically if you load babel with the option french.

## Global options

Sometimes, you want an option to be available to all of the packages you’ve loaded. That is done by giving it on the \documentclass line: every package can ‘see’ this list. So to pass the language of a document to all packages, we might use:

\documentclass[ngerman]{article} % Notice that the option name is 'ngerman'
\usepackage[T1]{fontenc}

\usepackage{babel}

\begin{document}

\tableofcontents

\section{"Uber "Apfel und Birnen}

\subsection{Äpfel}
Äpfel sind rot.

\subsection{Birnen}
Birnen sind gelb.

\end{document}


## More definitions

\newcommand allows commands with up to nine arguments, the first of which may be optional.

If we take the example from the main lesson, we could make the color optional, defaulting to blue.

\documentclass{article}
\usepackage[T1]{fontenc}

\usepackage{xcolor}

\newcommand\kw[2][blue]{\textcolor{#1}{\itshape #2}}

\begin{document}

\end{document}


Optional arguments are delimited with [] and if omitted, the default value specified in the definition is used.

## \NewDocumentCommand

From the October 2020 LaTeX release, an extended definition system is available. In older LaTeX releases this was available via the xparse package which we use here for compatibility.

We can repeat the above example but using \NewDocumentCommand

\documentclass{article}
\usepackage[T1]{fontenc}

\usepackage{xparse} % Only needed for older LaTeX releases
\usepackage{xcolor}

\NewDocumentCommand\kw{O{blue} m}{\textcolor{#1}{\itshape #2}}

\begin{document}


Just as with \newcommand, \NewDocumentCommand takes the command being defined (\kw here) and the definition body, using #1 to #9 for the arguments, however the difference is in how the arguments are specified.
Unlike \newcommand where just the number of arguments is given, optionally supplying a default for the first, with \NewDocumentCommand each argument is specified by a letter so a two argument command would be specified by {mm} rather than [2]. This is slightly more verbose but allows many more forms of commands to be defined. Here we just give this simple example where the first argument is optional, defaulting to blue (O{blue}) and the second argument is mandatory (m).