Indentation

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In plain TeX, controlling indentation is simple: The user sets a value for parindent, and each new paragraph is indented by that value, unless explicitly begun with noindent. Environments can provide a noindent at the end of their definitions, and if the user wants to overrule that, he can add an explicit indent at the beginning of the next paragraph. For the most part, LaTeX follows the same convention.

So, understanding indentation in plain TeX and LaTeX boils down to this: set a value for parindent, and start a new paragraph (i.e., leave an empty line) whenever you want indentation. For example, LaTeX usually does not indent the first line after a sectioning command. If you want to indent the first line after a sectioning command you use the indentfirst package (which is part of the required LaTeX bundle). If you want to indent the paragraph after an environment, you leave a blank line after the end of the environment; if you do not want to indent after the end of an environment, you do not leave a blank line. It takes a while to get used to, but the rules are easy to remember and eventually you do not need to even think about indentation; it becomes a matter of habit.

Indentations in ConTeXt are a bit different; and sometimes difficult to understand. In this article I hope to explain how ConTeXt does indentations. First, let's understand why ConTeXt does indentations differently; why does it not simply follow the time-tested approach of plain TeX and LaTeX? The way I understand it, the reason is that Hans Hagen, the author of ConTeXt, prefers spaced out markup — surrounding each environment by empty lines — which makes it easy to see where an environment starts and ends while reading the source file. However, this style means that the 'indentation after empty lines' paradigm of plain TeX and LaTeX cannot be used for indentations. So, ConTeXt provides an alternative. As with other things in ConTeXt, this alternative is consistent and easy to configure; but if you are used to other TeX formats it takes some time to get comfortable with it.

The basics

Setting up indentation for the whole document

Indentation involves two things: when to indent, and how much to indent. In ConTeXt, these can be specified using \setupindenting[...]. There are three types of keys for this command:

• To enable indenting: never or always, (equivalently, no or yes), The default is never

• To specify when to indent:: odd or even, and first or next. The default is first

• To specify how much to indent: none, small, medium, big, or a specific dimension. small corresponds to 1em, medium to 1.5em, and big to 2em. The default is none.

Suppose we want to indent all paragraphs by 20pt: we can use

\setupindenting[20pt, yes]

which is equivalent ot

\setupindenting[20pt, yes, first]

This is what one typically uses in a document. The other keys are needed only for special cases (like typesetting quotations and verses). In particular, the most commonly used keys are

• yes enable indenting
• no disable indenting
• toggle toggle the indenting state (if indenting was enabled, disable it and vice-versa)
• odd indents every odd paragraph
• even indents every even paragraph
• first indents all paragraphs, including the first paragraph
• next does not indent the first paragraph, but indents every subsequent paragraph
• reset reset all settings to their default values. This disable indenting, sets the indenting amount to none, disables odd or even indenting, and sets indenting method to first.

Setting up indentation after an environment

\setupindenting does not take care of indenting after environments, such as ConTeXt's itemizes, enumerations, definitions, formulas and floats. It also does not take care of indenting after heads such as chapters, sections, and subsections.

The setup command of these environments provides an indentnext key to configure the indentation behaviour after the environment. The indentnext key can take one of three values: yes, no, and auto. If indentnext=yes then the paragraph after the end of the environment is always indented; if indentnext=no then the next paragraph is never indented; if indentnext=auto then the next paragraph is indented only if there is a blank space after the environment. Setting indentnext=auto is equivalent to the default plain TeX and LaTeX behaviour.

Let us provide a couple of examples. Suppose we do not want paragraphs after itemize to be indented; then we can say

\setupitemgroup[itemize][indentnext=no]

If we want paragraphs after section heads to be indented, we can say

\setuphead[section][indentnext=yes]

If we want the paragraphs after all sectioning heads to be indented, we can say

\setupheads[indentnext=yes]

If we want paragraphs after formulas to be indented only if we leave a blank space after them, we can say

\setupformulas[indentnext=auto]

Setting up indentation inside environments

There is one case that is not taken care of by \setupindenting and the indentnext key: indentation of paragraphs inside multi-paragraph environments such as itemizes, descriptions, and enumerations. By default ConTeXt does not indent such paragraphs. The setup commands of these environments provides an indenting key to configure the indentation behaviour of paragraphs inside these environments. This key takes the same values as the arguments of \setupindenting command. For example, if we set

\setupitemgroup[itemize][indenting={40pt,next}]

then the following :

\setuppapersize[A5]

\setupindenting[medium,yes]
\setupitemgroup[itemize][indenting={40pt,next}]
\startitemize
\item This is an example of a multi|-|paragraph 
      item inside an itemize environment.

      This second paragraph is indented by 40pt
      (double the normal indentation).
\stopitemize

gives

Manual indentation

No matter how careful we are with all the settings, there are some cases which cannot be taken care of by automatic indentation, and we have to tell ConTeXt how to indent. Plain TeX (and LaTeX) provide the \indent and \noindent commands for explicitly indenting and preventing indenting of a paragraph. These commands are defined in ConTeXt but are not hooked into the ConTeXt indentation mechanism. Instead, ConTeXt provides \indentation and \noindentation which achieve the same effect.

Suppose the default setup for an article is

\setupitemgroup [itemize] [indentnext=no]

Now, if we want to indent after an itemize, starting the next paragraph with \indent does not work; to get indentation we have to say \indentation. For example,

\setuppapersize[A5]

\setupindenting [big,yes]
\setupitemgroup [itemize] [indentnext=no]

\startitemize[n]
    \item A dummy list
    \item To check \type{\indent}
\stopitemize

\indent This paragraph is not indented. The 
    \type{\indent} command does not work here.

\startitemize[n]
    \item Another dummy list
    \item To check \type{\indentation}
\stopitemize

\indentation This paragraph will be indented
    because we used \type{\indentation} instead.

gives

Beware of typos

ConTeXt defines two more commands not commonly used: \indenting and \noindenting. \indenting is similar to \setupindenting and is provided for backward compatibility; \noindenting is equivalent to [[Command/setupindenting[no]|\setupindenting[no]]]. Unfortunately, these commands sound very similar to \indentation and \noindentation, thus can be easily used by mistake. If you happen to write \noindenting instead of \noindentation in a document, it can take a while to debug.