How do conveniently control where description text starts?

Question

Consider a description list in which the body of a description is indented by some amount (\leftmargin I think). There are 3 obvious options for where the text of the first line of the description can begin:

1. At some fixed space from the end of the described term. (This is the default behavior.)
2. At \leftmargin on the same line as the described term, if possible, or on the next line otherwise.
3. Always at \leftmargin on the line below the defined term.

Here are option 1 and two ways of effecting option 3:

\documentclass{article}
\usepackage{lipsum}
\usepackage{calc}
\newcommand{\filledterm}[1]{%
  #1%
  \setlength{\mylength}{\textwidth-\widthof{#1}}%
  \hspace{\mylength}
}
\begin{document}
Plain vanilla:
\begin{description}
\item[One] \lipsum[4]
\item[And another one]  \lipsum[4]
\end{description}
With \verb|\mbox{}\\|:
\begin{description}
\item[One]\mbox{}\\  \lipsum[4]
\item[And another one]\mbox{}\\  \lipsum[4]
\end{description}
With filling:
\newlength{\mylength}
\begin{description}
\item[\filledterm{One}] \lipsum[4]
\item[\filledterm{And another one}] \lipsum[4]
\end{description}
\end{document}

Option 2 is a bit trickier, I guess I would need some kind of conditional in there.

Anyway, my question is - how can I actually avoid using these ugly hacks in each list separately? I want to be able to have some of my description lists behave one way, and others a different way. Do I need to patch the \item command somehow? ... but if I do that, it will effect all lists. I suppose I could use an \itemwrapper command in the relevant lists instead of \item, but I'd actually rather avoid that.

What would be a convenient-to-use (and hopefully elegant) way to let me choose which kind of placement I like for my description list?

Answer 1

Here is a demo of the basic description styles defined by enumitem, which can be further customised (font, left margin, &c.):

\documentclass{article}%
\usepackage[utf8]{inputenc} 
\usepackage[T1]{fontenc} 
\usepackage[svgnames]{xcolor}
\usepackage{lipsum}

\usepackage{enumitem}
\setlist[description]{leftmargin = 12mm}

\begin{document}

‘Force next line’: 
\begin{description}[labelwidth=\textwidth]
\item[One] \lipsum[4]
\item[And another one] \lipsum[4]
\end{description}

With \verb|style=sameline|:
\newlength{\mylength}
\begin{description}[style = sameline]
\item[One] \lipsum[4]
\item[And another one] \lipsum[4]
\end{description}

\newpage

With \verb|style=nextline, font=\itshape|:
\begin{description}[style =nextline, font=\normalfont\itshape]
\item[One] \lipsum[4]
\item[And another one] \lipsum[4]
\end{description}
With \verb|style=multiline, leftmargin=25mm|:
\begin{description}[style=multiline, leftmargin =25mm, font=\sffamily\color{Tomato}]
\item[One] \lipsum[4]
\item[And another one] \lipsum[4]
\end{description}

\end{document}