Answer by Gonzalo Medina for Automatic margin curly braces & text on multiple pages

Here's an option using tcolorbox instead of mdframed; this version takes care of all three requirements:

1. Uses braces.
2. Braces are placed on the outer margin.
3. The box has a width equal to the \textwidth; the braces are in the margin area.

The code:

\documentclass{scrbook}\usepackage{fontspec,collect,multido,lipsum}\usepackage{changepage}\strictpagecheck\newcounter{extrait}\newcounter{fiche}\usepackage[framemethod=tikz,usetwoside]{mdframed}\usepackage[many]{tcolorbox}\usetikzlibrary{calc,arrows,decorations.pathreplacing}\newtcolorbox{tcbdecor}[1]{  check odd page,  breakable,  colback=white,  boxrule=0pt,  colframe=white,  arc=0pt,  outer arc=0pt,  top=0pt,  bottom=0pt,  enhanced jigsaw,  oversize,  overlay={    \ifoddpage       \draw[decoration=brace,decorate,line width=1pt]         (frame.north east) -- node[rotate=270,above=4pt] {... #1 ...} (frame.south east);    \else      \draw[decoration={brace,mirror},decorate,line width=1pt]         (frame.north west) -- node[rotate=90,above=4pt] {... #1 ...} (frame.south west);    \fi  },}\newcommand\histoire[2]{%  \addtocounter{fiche}{1}%  \definecollection{his\thefiche}%  \begin{tcbdecor}{#1}  \begin{collect*}%    {his\thefiche}{}{}%    {\minisec{Extrait \addtocounter{extrait}{1}\theextrait : #1}}     {}   #2  \end{collect*}%  \end{tcbdecor}%}\begin{document}\chapter{Tests}\histoire{A}{\lipsum[1-3]}\lipsum[4]\histoire{B}{\lipsum[5-7]}\lipsum[8]\histoire{C}{\lipsum[9-16]}\chapter{Restitutions}\multido{\i=0+1}{\thefiche}{\setcounter{fiche}{1}\addtocounter{fiche}{\i}\includecollection{his\thefiche}}\end{document}

The result:

A zoomed-in image showing one of the boxes on an odd numbered page:

A zoomed-in image showing one of the boxes on an even numbered page:

If you want brackets instead, simply change the overlay section to

  overlay={    \ifoddpage       \draw[line width=1pt]         ([xshift=-5pt]frame.north east) -- (frame.north east) -- node[rotate=270,above=4pt] {... #1 ...} (frame.south east) -- ([xshift=-5pt]frame.south east);    \else      \draw[line width=1pt]         ([xshift=5pt]frame.north west) -- (frame.north west) -- node[rotate=90,above=4pt] {... #1 ...} (frame.south west) -- ([xshift=5pt]frame.south west);    \fi  },

With the above example, one now gets

on an odd numbered page, and

on an even numbered one.