Vertical line next to a block, across page breaks

Question

I'd like to mark examples, in an example environment in the text by drawing a vertical bar along the margin. I found a piece of code that uses the framed package to do this, but since the content of the environment in a box, this doesn't break across pages.

To show the example will continue on the next page, the line should extend vertically a bit further before/after the page break. That shouldn't be a problem using tikz, if one manages to place coordinates at the first/last lines of the environment and at the lines before/after each page break. It looks like Martin Scharrer was working on something like this, but I haven't found if that's ended up in a package by now…

In my case, I need support for at most one page break per environment.

Answer 1

As Davis Carlisle mentions in a comment, the mdframed package offers you a nice possibile solution, through its \newmdtheoremenv command; a little example interacting with one theorem style from amsthm:

\documentclass{article}
\usepackage[a5paper]{geometry}% just for the example
\usepackage{xcolor}
\usepackage{amsthm}
\usepackage[framemethod=tikz]{mdframed}
\usepackage{lipsum}% just to generate text for the example

\theoremstyle{remark}
\newmdtheoremenv[
  skipabove=\topsep,
  skipbelow=\topsep,
  innertopmargin=0pt,
  innerbottommargin=0pt,
  leftmargin=-13pt,
  splitbottomskip=2ex,
  splittopskip=3ex,
  linecolor={cyan!80!black},
  topline=false,
  leftline=true,
  bottomline=false,
  rightline=false,
  innerrightmargin=0pt,
  innerlinewidth=3pt
  font=\normalfont
]{example}{Example}

\begin{document}

\lipsum[1]
\begin{example}
\lipsum[1-4]
\end{example}
\lipsum[1]

\end{document}