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8.16 list

Synopsis:

\begin{list}{labeling}{spacing}
  \item[optional label of first item] text of first item
  \item[optional label of second item] text of second item
  ...
\end{list}

An environment for constructing lists.

Note that this environment does not typically appear in the document body. Most lists created by LaTeX authors are the ones that come standard: the description, enumerate, and itemize environments (see description, enumerate, and itemize).

Instead, the list environment is most often used in macros. For example, many standard LaTeX environments that do not immediately appear to be lists are in fact constructed using list, including quotation, quote, and center (see quotation & quote, see center).

This uses the list environment to define a new custom environment.

\newcounter{namedlistcounter}  % number the items
\newenvironment{named}
  {\begin{list}
     {Item~\Roman{namedlistcounter}.} % labeling 
     {\usecounter{namedlistcounter}   % set counter
      \setlength{\leftmargin}{3.5em}} % set spacing 
  }
  {\end{list}}

\begin{named}
  \item Shows as ``Item~I.''
  \item[Special label.] Shows as ``Special label.''
  \item Shows as ``Item~II.''
\end{named}

The mandatory first argument labeling specifies the default labeling of list items. It can contain text and LaTeX commands, as above where it contains both ‘Item’ and ‘\Roman{...}’. LaTeX forms the label by putting the labeling argument in a box of width \labelwidth. If the label is wider than that, the additional material extends to the right. When making an instance of a list you can override the default labeling by giving \item an optional argument by including square braces and the text, as in the above \item[Special label.]; see \item.

The mandatory second argument spacing has a list of commands. This list can be empty. A command that can go in here is \usecounter{countername} (see \usecounter). Use this to tell LaTeX to number the items using the given counter. The counter will be reset to zero each time LaTeX enters the environment, and the counter is incremented by one each time LaTeX encounters an \item that does not have an optional argument.

Another command that can go in spacing is \makelabel, which constructs the label box. By default it puts the contents flush right. Its only argument is the label, which it typesets in LR mode (see Modes). One example of changing its definition is that to the above named example, before the definition of the environment add \newcommand{\namedmakelabel}[1]{\textsc{#1}}, and between the \setlength command and the parenthesis that closes the spacing argument also add \let\makelabel\namedmakelabel. Then the items will be typeset in small caps. Similarly, changing the second code line to \let\makelabel\fbox puts the labels inside a framed box. Another example of the \makelabel command is below, in the definition of the redlabel environment.

Also often in spacing are commands to redefine the spacing for the list. Below are the spacing parameters with their default values. (Default values for derived environments such as itemize can be different than the values shown here.) See also the figure that follows the list. Each is a length (see Lengths). The vertical spaces are normally rubber lengths, with plus and minus components, to give TeX flexibility in setting the page. Change each with a command such as \setlength{itemsep}{2pt plus1pt minus1pt}. For some effects these lengths should be zero or negative.

\itemindent

Extra horizontal space indentation, beyond leftmargin, of the first line each item. Its default value is 0pt.

\itemsep

Vertical space between items, beyond the \parsep. The defaults for the first three levels in LaTeX’s ‘article’, ‘book’, and ‘report’ classes at 10 point size are: 4pt plus2pt minus1pt, \parsep (that is, 2pt plus1pt minus1pt), and \topsep (that is, 2pt plus1pt minus1pt). The defaults at 11 point are: 4.5pt plus2pt minus1pt, \parsep (that is, 2pt plus1pt minus1pt), and topsep (that is, 2pt plus1pt minus1pt). The defaults at 12 point are: 5pt plus2.5pt minus1pt, \parsep (that is, 2.5pt plus1pt minus1pt), and \topsep (that is, 2.5pt plus1pt minus1pt).

\labelsep

Horizontal space between the label and text of an item. The default for LaTeX’s ‘article’, ‘book’, and ‘report’ classes is 0.5em.

\labelwidth

Horizontal width. The box containing the label is nominally this wide. If \makelabel returns text that is wider than this then the first line of the item will be indented to make room for this extra material. If \makelabel returns text of width less than or equal to \labelwidth then LaTeX’s default is that the label is typeset flush right in a box of this width.

The left edge of the label box is \leftmargin+\itemindent-\labelsep-\labelwidth from the left margin of the enclosing environment.

The default for LaTeX’s ‘article’, ‘book’, and ‘report’ classes at the top level is \leftmargini-\labelsep, (which is 2em in one column mode and 1.5em in two column mode). At the second level it is \leftmarginii-\labelsep, and at the third level it is \leftmarginiii-\labelsep. These definitions make the label’s left edge coincide with the left margin of the enclosing environment.

\leftmargin

Horizontal space between the left margin of the enclosing environment (or the left margin of the page if this is a top-level list), and the left margin of this list. It must be non-negative.

In the standard LaTeX document classes, a top-level list has this set to the value of \leftmargini, while a list that is nested inside a top-level list has this margin set to \leftmarginii. More deeply nested lists get the values of \leftmarginiii through \leftmarginvi. (Nesting greater than level five generates the error message ‘Too deeply nested’.)

The defaults for the first three levels in LaTeX’s ‘article’, ‘book’, and ‘report’ classes are: \leftmargini is 2.5em (in two column mode, 2em), \leftmarginii is 2.2em, and \leftmarginiii is 1.87em.

\listparindent

Horizontal space of additional line indentation, beyond \leftmargin, for second and subsequent paragraphs within a list item. A negative value makes this an “outdent”. Its default value is 0pt.

\parsep

Vertical space between paragraphs within an item. In the ‘book’ and ‘article’ classes The defaults for the first three levels in LaTeX’s ‘article’, ‘book’, and ‘report’ classes at 10 point size are: 4pt plus2pt minus1pt, 2pt plus1pt minus1pt, and 0pt. The defaults at 11 point size are: 4.5pt plus2pt minus1pt, 2pt plus1pt minus1pt, and 0pt. The defaults at 12 point size are: 5pt plus2.5pt minus1pt, 2.5pt plus1pt minus1pt, and 0pt.

\partopsep

Vertical space added, beyond \topsep+\parskip, to the top and bottom of the entire environment if the list instance is preceded by a blank line. (A blank line in the LaTeX source before the list changes spacing at both the top and bottom of the list; whether the line following the list is blank does not matter.)

The defaults for the first three levels in LaTeX’s ‘article’, ‘book’, and ‘report’ classes at 10 point size are: 2pt plus1 minus1pt, 2pt plus1pt minus1pt, and 1pt plus0pt minus1pt. The defaults at 11 point are: 3pt plus1pt minus1pt, 3pt plus1pt minus1pt, and 1pt plus0pt minus1pt). The defaults at 12 point are: 3pt plus2pt minus3pt, 3pt plus2pt minus2pt, and 1pt plus0pt minus1pt.

\rightmargin

Horizontal space between the right margin of the list and the right margin of the enclosing environment. Its default value is 0pt. It must be non-negative.

\topsep

Vertical space added to both the top and bottom of the list, in addition to \parskip (see \parindent & \parskip). The defaults for the first three levels in LaTeX’s ‘article’, ‘book’, and ‘report’ classes at 10 point size are: 8pt plus2pt minus4pt, 4pt plus2pt minus1pt, and 2pt plus1pt minus1pt. The defaults at 11 point are: 9pt plus3pt minus5pt, 4.5pt plus2pt minus1pt, and 2pt plus1pt minus1pt. The defaults at 12 point are: 10pt plus4pt minus6pt, 5pt plus2.5pt minus1pt, and 2.5pt plus1pt minus1pt.

This shows the horizontal and vertical distances.

latex2e-figures/list

The lengths shown are listed below. The key relationship is that the right edge of the bracket for h1 equals the right edge of the bracket for h4, so that the left edge of the label box is at h3+h4-(h0+h1).

v0

\topsep + \parskip if the list environment does not start a new paragraph, and \topsep+\parskip+\partopsep if it does

v1

\parsep

v2

\itemsep+\parsep

v3

Same as v0. (This space is affected by whether a blank line appears in the source above the environment; whether a blank line appears in the source below the environment does not matter.)

h0

\labelwidth

h1

\labelsep

h2

\listparindent

h3

\leftmargin

h4

\itemindent

h5

\rightmargin

The list’s left and right margins, shown above as h3 and h5, are with respect to the ones provided by the surrounding environment, or with respect to the page margins for a top-level list. The line width used for typesetting the list items is \linewidth (see Page layout parameters). For instance, set the list’s left margin to be one quarter of the distance between the left and right margins of the enclosing environment with \setlength{\leftmargin}{0.25\linewidth}.

Page breaking in a list structure is controlled by the three parameters below. For each, the LaTeX default is -\@lowpenalty, that is, -51. Because it is negative, it somewhat encourages a page break at each spot. Change it with, e.g., \@beginparpenalty=9999; a value of 10000 prohibits a page break.

\@beginparpenalty

The page breaking penalty for breaking before the list (default -51).

\@itempenalty

The page breaking penalty for breaking before a list item (default -51).

\@endparpenalty

The page breaking penalty for breaking after a list (default -51).

The package enumitem is useful for customizing lists.

This example has the labels in red. They are numbered, and the left edge of the label lines up with the left edge of the item text. See \usecounter.

\usepackage{color}
\newcounter{cnt}  
\newcommand{\makeredlabel}[1]{\textcolor{red}{#1.}}
\newenvironment{redlabel}
  {\begin{list}
    {\arabic{cnt}}
    {\usecounter{cnt}
     \setlength{\labelwidth}{0em}
     \setlength{\labelsep}{0.5em}
     \setlength{\leftmargin}{1.5em}
     \setlength{\itemindent}{0.5em} % equals \labelwidth+\labelsep
     \let\makelabel=\makeredlabel
    }
  }
{\end{list} }

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