Control page breaks in multiple frames via mdframed

Question

I am having an issue with mdframed, where I've created a frames inside frames spanning several pages, but I'd like mdframed to split them differently across the pages, so as much of the text on page two is moved to page one.

Here is the output of the code:

The desired result should look like this, which I've created in Microsoft Paint:

Here is the code:

\documentclass{article}
\usepackage{mdframed,lipsum}
\newmdenv[
leftmargin = 0pt,
innerleftmargin = 1em,
innertopmargin = 0pt,
innerbottommargin = 0pt,
innerrightmargin = 0pt,
rightmargin = 0pt,
linewidth = 1pt,
topline = false,
rightline = false,
bottomline = false
]{leftbar}
\begin{document}
\lipsum[1]
\begin{leftbar}
    \lipsum[2]
    \begin{leftbar}
        \lipsum[3-5]
    \end{leftbar}
\end{leftbar}
\end{document}

---

Update: There is another issue, where the frame exceeds the page margins:

One can see the page number on top of the frame in the image. I'd like for the frame to break across pages and stay inside the page margins. The result was obtained by changing \lipsum[3-5] to \lipsum[3-20] in the previous MWE.

Answer 1

You can use another macros than mdframed for your purpose. For example the following macros:

\documentclass{article}
\usepackage{lipsum}

\newcount\tmpnum
\def\leftline{\par \setbox0=\vbox\bgroup \advance\leftskip by1em \noindent\ignorespaces}
\def\endleftline{\par \setbox1=\vbox{}\endleftlineA}
\def\endleftlineA{
   \setbox0=\lastbox
   \ifvoid0 \expandafter \endleftlineB \else
   \global\dimen1=\ht0
   \dimen0=\lastskip \unskip \advance\dimen0 by\lastskip \unskip
   \tmpnum=\lastpenalty \unpenalty
   \global\setbox1=\vbox{\ifnum\tmpnum=0 \else \penalty\tmpnum \fi
      \vskip\dimen0 \hbox{\hbox to\leftskip{\hss\leftrule\kern.4em}\kern-\leftskip\box0}
      \unvbox1}
   \expandafter \endleftlineA \fi
}
\def\endleftlineB{\egroup \advance\dimen1 by\prevdepth
   \advance\dimen1 by-\baselineskip
   \vskip-\dimen1 \unvbox1
}
\def\leftrule{\vbox{\kern-.7\baselineskip
   \hbox{\vrule width1pt height.7\baselineskip depth\ifdim\ht1>0pt.4\else.1\fi\baselineskip}
   \kern-\prevdepth}
}


\begin{document}
\lipsum[1]
\leftline
    \lipsum[2]
    \leftline
        \lipsum[3-6]
    \endleftline
\endleftline
\lipsum[1]

\end{document}

Answer 2

After closer inspection of the manual I found the following text:

A nested mdframed environment can’t be splitted.

That explains it.