How to switch between two margin sizes?

Question

This question led to a new package:
fullwidth

This is a followup to a similar question. The idea is to switch between two different margin sizes. The answer provided by @godbyk work very well. However, it is difficult if you are using an asymmetric page layout (e.g. \documentclass[twoside]{article} and the fullwidth environment spans over two pages. Is it possible to make it work in these cases, too?

The memoir manual states:

Note that the adjustwidth environment applies to complete paragraphs; you can’t change the width of part of a paragraph except for hanging paragraphs or more esoterically via \parshape. Further, if the adjusted paragraph crosses a page boundary the margin changes are constant; a paragraph that is, say, wider at the right on the first page will also be wider at the right as it continues onto the following page.

So, how to do it esoterically ;)

MWE:

\documentclass[twoside]{article}

\usepackage{changepage}% provides the adjustwidth environment

% The following code should be used *after* any changes to the margins and
% page layout are made (e.g., after the geometry package has been loaded).
\newlength{\fullwidthlen}
\setlength{\fullwidthlen}{\marginparwidth}
\addtolength{\fullwidthlen}{\marginparsep}

\newenvironment{fullwidth}{%
  \begin{adjustwidth*}{}{-\fullwidthlen}%
}{%
  \end{adjustwidth*}%
}

\usepackage{lipsum}% provides dummy text

\begin{document}

\lipsum[1]

\begin{fullwidth}
    \lipsum[2-10]
\end{fullwidth}

\lipsum[3]

\end{document}

Answer 1

The new package fullwidth is uploaded to CTAN. The development status is available on github.

\setcounter{errorcontextlines}{999}
\documentclass[twoside]{article}
\usepackage{showframe,lipsum}
\usepackage[innermargin=-2.0cm,]{fullwidth}
\begin{document}
\lipsum

%\clearpage
\begin{fullwidth}[width=\linewidth+2cm]
Start\par
\lipsum[1] \lipsum \lipsum
ENDE
\end{fullwidth}
\end{document}

---

Are you looking for somethink like the following example?

\documentclass[twoside]{article}
%\usepackage{showframe}
\usepackage{mdframed}
\usepackage{lipsum}
\begin{document}

\lipsum[1]

\begin{mdframed}[outermargin=\dimexpr-\marginparwidth-\marginparsep\relax,innermargin=0pt]
    \lipsum[2-10]
\end{mdframed}

\lipsum[3]
\end{document}