Putting a bar in the margin

Question

I sometimes want to give examples in a document I am writing. Because these examples are quite general it could be difficult for readers to see the difference between the examples and the theoretical analysis. Therefore I want to put a long vertical bar (that spans the entire example) in the margin indicating the text next to it is an example. It could be that the example uses two pages or more.

Is there any helpful package to do this. An environment would be fine. Something like this:

\begin{example}
...
\end{example}

Other suggestions to indicate the difference are welcome too. First I thought using a different background color. But I want to keep the document printable in Black/White and reading text with a gray background isn't that easy. A horizontal line at the begin and end is also an option but after two pages people could get confused.

Answer 1

The framed package provides a leftbar environment that does something like what you want:

\documentclass{article}
\usepackage{framed,lipsum}
\begin{document}
\lipsum[1]
\begin{leftbar}
This is a test.
\end{leftbar}
\lipsum[2]
\end{document}

Answer 2

You can also use PDF annotations with the pdfcomment package

\documentclass{scrartcl}
\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{lipsum}
\usepackage[svgnames,rgb]{xcolor}
\usepackage[subject={Top1},author={Josef}]{pdfcomment}
\begin{document}
\begin{pdfsidelinecomment}[color=red,icolor=yellow,caption=inline,linebegin={/Butt},lineend={/Square},linewidth=2bp,linesep=1cm]{Example}
\lipsum[2]
\end{pdfsidelinecomment}
\end{document} 

Answer 3

Have a look at changebar package: https://ctan.org/pkg/changebar

An example:

\documentclass{article}
\usepackage[color]{changebar}
\cbcolor{blue}
\usepackage{lipsum}% for random text only
\begin{document}

\cbstart
\lipsum[1]
\cbend

\lipsum[2]
\end{document}

Answer 4

mdframed provides a flexible way of adding a (partial) frame around a block of content:

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

\lipsum[1]

\begin{leftbar}
\lipsum[2]
\end{leftbar}

\lipsum[3]

\end{document}

The above output is similar to what is achieved using the leftbar package.

Answer 5

Another possibility for indicating an example: If your document has anything to do with code, you might want to consider use of \verb and the verbatim environment. All it does is place the example in monospaced font, and it's wysiwyg. So you can also type up LaTeX examples as-is. I use the \verb command for short, in-line examples, and the verbatim environment for longer ones like this:

\documentclass{article}
\begin{document}

This is the explanation for the \verb#lambda# function:
\begin{verbatim}
>>> #this is a comment 
...
>>> sq = lambda x: x**2
>>> sq(2)
\end{verbatim}
will return \verb#4#.

\end{document}

produces this:

Note you don't have to use ## to delimit the \verb command, you can use another pair, like !!.

Answer 6

Another option comes from the package thmbox, which provide a leftbar environment.

\documentclass{article}
\usepackage{thmbox}
\usepackage{lipsum}
\begin{document}
\lipsum[1]
\begin{leftbar}
  \lipsum[2]
\end{leftbar}
\lipsum[3]
\end{document}