How do I draw a line on the INNER margin in a double-sided document?

Question

With the mdframed package one can draw nice lines on the left or right of the text. For example:

\documentclass[a4paper,twoside,11pt]{article}

\usepackage[framemethod=TikZ]{mdframed} 

\mdfdefinestyle{MDFStyGrayBar}{%
    linecolor=gray,
    backgroundcolor=white,
    %
    outerlinewidth=5pt,
    %
    topline=false,
    bottomline=false,
    rightline=false,
    leftline=true,
    %
    innertopmargin=4pt, %\baselineskip
    innerbottommargin=8pt,
    innerrightmargin=3pt,
    innerleftmargin=3pt,
    %
    skipabove=\topskip,
    skipbelow=\topskip
}

\begin{document}

\noindent Some normal text.
\begin{mdframed}[style=MDFStyGrayBar]
Some text with a vertical bar on the left.
\end{mdframed}

\end{document}

looks like this:

But what if I want the line to be on the inner side in a double-sided ("twoside") document? That is, on the left for a right-page and on the right for a left-page? This should also work, when the frame extends over several pages. Is that possible with the mdframed package?

Thanks for your help!

Answer 1

mdframed detects whether it is used inside twoside mode. If it's true you can adjust length by innermargin and outermargin. The hack below adds some options to the original definition. If you are on an odd page the setting \mdfsetup{hidealllines=true,leftline=true} is used. On the other hand \mdfsetup{hidealllines=true,rightline=true} is used.

\documentclass[a4paper,twoside,11pt]{article}

\usepackage[framemethod=TikZ]{mdframed} 
\makeatletter
\newrobustcmd*\if@mdf@pageodd@bar{%
 \zref@refused{mdf@pagelabel-\the\value{mdf@zref@counter}}%
 \ifodd\zref@extract{mdf@pagelabel-\the\value{mdf@zref@counter}}%
                    {mdf@pagevalue}%
    \setlength\mdf@rightmargin@length{\mdf@outermargin@length}%
    \setlength\mdf@leftmargin@length{\mdf@innermargin@length}%
    \mdfsetup{hidealllines=true,leftline=true}%
 \else
    \setlength\mdf@rightmargin@length{\mdf@innermargin@length}%
    \setlength\mdf@leftmargin@length{\mdf@outermargin@length}%
    \mdfsetup{hidealllines=true,rightline=true}%
 \fi%
}
\newrobustcmd*\changepageodd{\let\if@mdf@pageodd\if@mdf@pageodd@bar}
\makeatother
\mdfdefinestyle{MDFStyGrayBar}{%
    linecolor=gray,
    backgroundcolor=white,
    %
    outerlinewidth=5pt,
    %
    topline=false,
    bottomline=false,
    rightline=false,
    leftline=true,
    %
    innertopmargin=4pt, %\baselineskip
    innerbottommargin=8pt,
    innerrightmargin=3pt,
    innerleftmargin=3pt,
    %
    skipabove=\topskip,
    skipbelow=\topskip,
    settings={\changepageodd}
}
\usepackage{showframe,lipsum}
\begin{document}

\noindent Some normal text.
\begin{mdframed}[style=MDFStyGrayBar]
\lipsum
\end{mdframed}

\end{document}