355. LaTeX技巧303：description列表不得不说的用法

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在我个人使用经验里，Description 用的不很多，作为LaTeX列表的一个典型。我研读了一下，也发现如下几个问题，希望对您的使用有所帮助。
基本用法
首先看一个Description的示例。
\begin{description}
\item[First Item] This is a shorter item label, and some text that talks about it.
The text is wrapped into a paragraph, with successive lines indented.

This is another paragraph under the item.
\begin{description}
\item[Sub-Item] This is a description of an item which is within the
first item.
\item[Sub-Item] Another sub-item.
\end{description}
\item[Second Item] Another item that's not part of above item.
\end{description}
description顾名思义，对列表项的解释描述等，description项描述可以是多个段落，也可多个环境嵌套。
显示结果为：

有时，这样使用description觉得不是很符合我们的使用习惯。
第一，让label 项换行显示如何设置？
解决方法：\begin{description}
\item[{\parbox[t]{3cm}{first line\\second line}}] This is a shorter item label, and some text that talks about it.
The text is wrapped into a paragraph, with successive lines indented.
\end{description}
但是这会影响，后面文字的格式，目前我没找到更好的解决方案，欢迎您提供。
第二，如何让描述文字另起一行进行描述？
解决方案列举如下：
（1）采用横向填充。
\begin{description}
\item[Very long label] \hspace*{\fill} \\
Text...
\end{description}
\begin{description}
\item[First] \hfill \\
The first item
\item[Second] \hfill \\
The second item
\end{description}
（2）使用enumitem宏包，定义labelsep。
\usepackage{enumitem}
\setdescription{labelsep=\textwidth}
（2）这是下下之策，重新定义Description即可，推荐上述两个方法。

\let\origdescription\description
\renewenvironment{description}{

  \setlength{\leftmargini}{0em}

  \origdescription

  \setlength{\itemindent}{0em}

  \setlength{\labelsep}{\textwidth}
}
{\endlist}

第三个问题是要label项是同样宽度，不要总是或长或短。
解决方案：
（1）使用mdwlist宏包，较为简便
\usepackage{mdwlist}
\begin{basedescript}{\desclabelstyle{\pushlabel}\desclabelwidth{10em}}
\item[Short] This is a shorter item label, and some text that talks about it.
The text is wrapped into a paragraph, with successive lines indented.

The another paragraph within one item.
\item[Rather longer label] This is a longer item label. As you can see, the
text is not started a specified distance in -- unlike with other lists -- but
is spaced a fixed distance from the end of the label.
\end{basedescript}
结果图：

（2）利用list环境定义自己的描述环境如下：
\usepackage{calc}
\newenvironment{altDescription}[1]
{\begin{list}{}%
{\renewcommand\makelabel[1]{\textsf{##1:}\hfil}%
\settowidth\labelwidth{\makelabel{#1}}%
\setlength\leftmargin{\labelwidth+\labelsep}}}%
{\end{list}}
\begin{altDescription}{Return values}
\item[Description]
Returns from a function. If issued at top level,
the interpreter simply terminates, just as if end
of input had been reached.
\item[Errors]
None.
\item[Return values]
Any arguments in effect are passed back to the
caller.
\end{altDescription}
需要自己提供最宽单词的参数。

第四个问题：Description如何让描述部分缩进都相同呢？
参见：http://bbs.chinatex.org/forum.php?mod=viewthread&tid=3689&page=1&extra=#pid9925
第五个问题：Description如何让label带有缩进呢？
使用eqlist 宏包
\usepackage{eqlist}
\begin{quote}
\begin{eqlist*}[\eqliststarinit\def\makelabel#1{#1}\labelsep1em]
\item[$D$] is the diffusion coefficient of solute molecules moving from the bulk liquid to the crystal surface,
\item[$t$] is time,
\item[$\lambda$] is a rate constant, that increases with increasing supersaturation.
\end{eqlist*}
\end{quote}