Is there a pre-defined width that covers the text area and the margin?

Question

Is there a pre-defined width that covers both the text and margin areas? Correct me if I am wrong, but it would basically be equal to \textwidth+\marginparsep+\parginparwidth.

Is that provided by LaTeX somewhere?

If not, I am currently defining it this way in the preamble:

\newlength{\widewidth}
\setlength{\widewidth}{\textwidth+\marginparsep+\marginparwidth}

Is that the right approach? Are there any caveats? For example, if I change a page's orientation, would \widelength change its size to reflect that?

Answer 1

Once a user length is defined, it is fixed in physical units until reset by the user (see Defining a Length that Scales with Fontsize Changes). So the way you define a "length" that can adjust with page dimension changes is to define it as a macro \def in terms of the system lengths that are updated with format changes, rather than as a \setlength which will fix the length. In this manner, the \def is re-evaluated to its "current" value at every invocation.

Once that lesson is learned, the next aspect to your question is that \linewidth rather than \textwidth is the appropriate length to use when, for example, changing into landscape mode, etc. On page 1 of my MWE, it makes no difference which is used, but on page 2, one can see that the \linewidth definition gives the proper result, not the \textwidth result.

And finally, if \reversemarginpar is used, as is done on page 3 of the MWE, then extra provisions must be made

\documentclass{article}
\usepackage[demo]{graphicx}
\usepackage{pdflscape}
\usepackage[nopar]{lipsum}
  \def\wrongwidewidth{\dimexpr\textwidth+\marginparsep+\marginparwidth}%
  \def\rightwidewidth{\dimexpr\linewidth+\marginparsep+\marginparwidth}%
\begin{document}
\lipsum[1]\marginpar{This is a test of a margin par}\vspace{2cm}\par
Doesn't matter\par
\noindent\includegraphics[width=\wrongwidewidth]{test}

Doesn't matter\par
\noindent\includegraphics[width=\rightwidewidth]{test}
\begin{landscape}
  \lipsum[2]\marginpar{This is a test of a margin par}\vspace{2cm}\par
  Wrong\par
  \noindent\includegraphics[width=\wrongwidewidth]{test}

  Right\par
  \noindent\includegraphics[width=\rightwidewidth]{test}
\end{landscape}

With reverse marginpar, tricks must be done\vspace{2cm}\par\reversemarginpar
\lipsum[1]\marginpar{This is a test of a margin par}\vspace{2cm}\par
Doesn't matter\par
\noindent\makebox[\linewidth][r]{\includegraphics[width=\wrongwidewidth]{test}}

Doesn't matter\par
\noindent\makebox[\linewidth][r]{\includegraphics[width=\rightwidewidth]{test}}
\end{document}