Underlining an item

Question

Is there a way to allow a new item inside an underline command? In my real work, I have a custom command generating the "item" with its text, so moving the \underline to the other side of the \item isn't an option. Here's a MWE:

\documentclass{article}
\begin{document}
\begin{itemize}
\underline{\item abcd}
\end{itemize}
\end{document}

The error message I get is "Something's wrong - perhaps a missing \item".

Edit: Here's a less minimal working example:

\documentclass{article}
\usepackage{lipsum}

\newcommand{\course}[3]{\item[MATH #1] \emph{#2}\newline{#3}}

\newcommand{\sixten}{\course{610}{A Course Title}{A long description \lipsum[5]}}
\newcommand{\sixtwenty}{\course{620}{Another Course Title}{A shorter description}}

\begin{document}

{\large Course Offerings:}

Fall 2016
\begin{description}
\sixten
\sixtwenty
\end{description}

Spring 2017
\begin{description}
\underline{\sixten}
\sixtwenty
\end{description}
\end{document}

Answer 1

I propose this, with the help of the framed package, slightly tweaking the leftbar environment. If you don't want grey lines, it's easy to remove the colour. Using xparse, I define a \course command, with $3$ mandatory arguments. A star version adds a left bar that can beak across pages:

\documentclass{article}
\usepackage{lipsum}
\usepackage{framed, xcolor, xparse}

\renewenvironment{leftbar}{%
  \def\FrameCommand{{\hspace{20pt}\color{lightgray}\vrule width 2pt}\hspace{-18pt}}%
  \MakeFramed {\advance\hsize-2\width \FrameRestore}}%
 {\endMakeFramed}

\DeclareDocumentCommand\course{ s m m +m }{%
\item[MATH #2] \emph{#3}\newline{%
\IfBooleanTF{#1}{\setlength\OuterFrameSep{-\topsep} \begin{leftbar}#4\end{leftbar}}%
{#4}}%
}

\newcommand{\sixtwenty}{\course{620}{Another Course Title}{A shorter description}}

\begin{document}

{\large Course Offerings:}\bigskip

Fall 2016
\begin{description}
\course*{610}{A Course Title}{A long description \lipsum[5]}
\sixtwenty
\end{description}

Spring 2017
\begin{description}

\course{610}{A Course Title}{A long description \lipsum[5]}
\sixtwenty
\end{description}

\end{document} 

Answer 2

Here's a way of drawing the left bar suggested by Bernard when a star is appended to the command. It requires defining new courses with \newcourse rather than \newcommand, but it involves less typing as an added bonus.

• \newcourse{\newcommandname}{<number>}{<title>}{<description>} sets up a new course. It will create \newcommandname which will create the regular print of the course and \newcommandname* which will add a left bar in the margin.

• \setlength\courselinewidth{<width>} controls the width of the line.

• The colour and opacity of the line can be set with \coursehighlight[<colour>]{<% opacity>}. The default colour is black. Below, I show how to set the opacity and colour in a couple of ways, including one which is there just in case you get a colour printer and fancy a change.

Note that this will not work in the case that a page break occurs during the highlighted course, and no attempt is made to prevent or detect this.

Here are three examples:

Code:

\documentclass{article}
\usepackage{xparse,tikz,tikzpagenodes}
\usetikzlibrary{tikzmark,calc}
\usepackage{lipsum}
\newcounter{hcourse}
\setcounter{hcourse}{0}
\newcommand{\course}[3]{\item[MATH #1] \emph{#2}\par #3}
\NewDocumentCommand\newcourse { m m m +m }{%
  \NewDocumentCommand #1 { s }{%
    \IfBooleanTF ##1 {%
      \stepcounter{hcourse}%
      \course{\tikzmark{\thehcourse a}#2}{#3}{#4}\tikzmark{\thehcourse b}%
      \tikz[remember picture, overlay]{%
        \foreach \i in {a,b} \coordinate (\thehcourse \i) at ({pic cs:\thehcourse \i});
        \draw [course highlight, line width=\courselinewidth] ($(\thehcourse a -| current page text area.west) + (-1em,\baselineskip)$) coordinate (\thehcourse c) -- ($(\thehcourse b -| \thehcourse c)$);
      }%
    }{%
      \course{#2}{#3}{#4}%
    }%
  }%
}
\NewDocumentCommand\coursehighlight { O {black} m }{%
  \colorlet{course highlight}{#1!#2}}
\newlength\courselinewidth
\setlength\courselinewidth{1pt}
\coursehighlight{75}
\newcourse{\sixten}{610}{A Course Title}{A long description \lipsum[5] Final words.}
\newcourse{\sixtwenty}{620}{Another Course Title}{A shorter description}

\begin{document}

\title{Course Offerings}
\author{}\date{}
\maketitle

\subsubsection*{Fall 2016}
\begin{description}
  \sixten
  \sixtwenty
\end{description}

\subsubsection*{Spring 2017}
\begin{description}
  \sixten*
  \sixtwenty
\end{description}

\coursehighlight[gray]{50}
\setlength\courselinewidth{1mm}
\begin{description}
  \sixten
  \sixtwenty*
\end{description}

In case you get a colour printer\dots
\coursehighlight[blue]{80}
\begin{description}
  \sixten*
  \sixtwenty
\end{description}
\end{document}

Original Answer (Corrected)

Here's a way of boxing the course when a star is appended to the command. It requires defining new courses with \newcourse rather than \newcommand, but it involves less typing as an added bonus.

\documentclass{article}
\usepackage{xparse,tikz,tikzpagenodes}
\usetikzlibrary{tikzmark,calc}
\usepackage{lipsum}
\newcounter{hcourse}
\setcounter{hcourse}{0}
\newcommand{\course}[3]{\item[MATH #1] \emph{#2}\par #3}
\NewDocumentCommand\newcourse { m m m +m }{%
  \NewDocumentCommand #1 { s }{%
    \IfBooleanTF ##1 {%
      \stepcounter{hcourse}%
      \course{\tikzmark{\thehcourse a}#2}{#3}{#4}\tikzmark{\thehcourse b}%
      \tikz[remember picture, overlay]{%
        \foreach \i in {a,b} \coordinate (\thehcourse \i) at ({pic cs:\thehcourse \i});
        \draw ($(\thehcourse a -| current page text area.west) + (-1em,\baselineskip)$) rectangle ($(\thehcourse b -| current page text area.east) + (1em,-.5\baselineskip)$);
      }%
    }{%
      \course{#2}{#3}{#4}%
    }%
  }%
}
\newcourse{\sixten}{610}{A Course Title}{A long description \lipsum[5] Final words.}
\newcourse{\sixtwenty}{620}{Another Course Title}{A shorter description}
\begin{document}

\title{Course Offerings}
\author{}\date{}
\maketitle

\subsubsection*{Fall 2016}
\begin{description}
  \sixten
  \sixtwenty
\end{description}

\subsubsection*{Spring 2017}
\begin{description}
  \sixten*
  \sixtwenty
\end{description}
\end{document}

Answer 3

Thanks to Bernard, I have the following solution:

\documentclass{article}
\usepackage{lipsum,framed}
\newcommand{\course}[3]{\item[MATH #1] \emph{#2}\newline{#3}}
\newcommand{\sixten}{\course{310}{A Course Title}{A long description \lipsum[5]}}
\newcommand{\sixtwenty}{\course{320}{Another Course Title}{A shorter description}}
\begin{document}
{\Large Course Offerings:}

Fall 2016
\begin{description}
\sixten
\sixtwenty
\end{description}
Spring 2017
\begin{description}
\begin{leftbar}
\sixten
\end{leftbar}
\sixtwenty
\end{description}
\end{document}