Indentation (typesetting)

In the written form of many languages, indentation describes empty space (white space) used before or around text to signify an important aspect of the text such as:

• Beginning of a paragraph
• Hierarchy Template:Endash subordinate concept
• Quotation

Many computer languages use block indentation to demarcate blocks of source code.

Indentation is essentially the same regardless of whether the writing system is left-to-right (e.g. Latin and Cyrillic) or right-to-left (e.g. Hebrew and Arabic) when considering line beginning and end. For example, indenting at the beginning of line means on the left for a left-to-right script and on the right for right-to-left script.

Indent is both a noun and a verb. The verb is the act of formatting text to be indented whereas the noun refers to the resulting empty space.

Types

There are three main types of indentation: first-line, hanging and block.

Each example below is in a box that represents the page boundary and uses the common typesetting lorem ipsum content. The width of indentation here is in units of em spaces.

Indentation in programming

In computer programming, indentation describes formatting source code with whitespace to the left of code text Template:Endash often to visually show that a sequence of code lines is syntactically a code block. Typically, the lines of a block are aligned with an amount of white space that indicates the block's depth in the hierarchical structure of the code. Each inner level of the hierarchy is indented by a multiple of this indentation width.

White space in code is typically stored as whitespace characters.

For a free-form language, indentation is exclusively for the programmer since a code processor (i.e. compiler, interpreter) ignores whitespace characters. Code can have inconsistent or even no indentation, but in general is formatted with somewhat consistent indentation.

Some languages rely on indentation to demarcate block structure, often via the off-side rule. Due to this syntax requirement, the code must have a level of consistency that is not required in free-form language code.

The neologisms outdent, unindent and dedent describe the opposite of indentation Template:Endash aligning code text of a line to the left of the previous line.

Variations

Common variations in the implementation of indentation include: how much to indent a block at each level of the code hierarchy, usually measured in spaces, and whether to store whitespace characters as space or tab characters. Although there are common practices, consensus is not universal. <ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> These variations are driven by factors that may include but are not limited to: language syntax, organizational mandate and personal preference.

Common practices

The following table identifies notable practices with respect to code indentation.

Language	Free-form?	Note
Bash	Template:Yes	citation	CitationClass=web }}</ref> Google uses 2 spaces <ref>{{#invoke:citation/CS1|citation	CitationClass=web }} </ref>
C	Template:Yes	The Linux kernel uses 1 tab<ref>{{#invoke:citation/CS1|citation	CitationClass=web }} </ref><ref> {{#invoke:citation/CS1|citation	CitationClass=web }} </ref> NASA uses 4 spaces.<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> Clinton Staley advocates 3 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>
C++	Template:Yes	citation	CitationClass=web }}</ref> Google uses 2 spaces<ref>[1] Template:Webarchive</ref>
C#	Template:Yes	Microsoft convention: 4 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>
CSS	Template:Yes	Drupal, GitHub, and Google use 2 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref name="google">{{#invoke:citation/CS1|citation	CitationClass=web }} This is an HTML-rendered copy of the official version, which is maintained in XML format</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> WordPress uses tabs<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>
Dart	Template:Yes	dart format uses 2 spaces
Delphi	Template:Yes	citation	CitationClass=web }}</ref>
F#	Template:Yes	citation	CitationClass=web }}</ref>
Go	Template:Yes	citation	CitationClass=web }}</ref>
Haskell	Template:No	citation	CitationClass=web }}</ref>
HTML	Template:Yes	Google uses 2 spaces<ref name="google" /> HTML Tidy defaults to 2 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>
Java	Template:Yes	Oracle uses 4 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> Android uses 4 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> Most Eclipse IDE components use tabs
JavaScript	Template:Yes	Douglas Crockford advocates 4 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> GitHub and Google use 2 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> jQuery uses tabs<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> Firefox's built-in jsbeautifier defaults to 2 spaces prettyprinter in Google Chrome and Internet Explorer use 4 spaces
Julia	Template:Yes	citation	CitationClass=web }}</ref>
Kotlin	Template:Yes	citation	CitationClass=web }}</ref>
Lua	Template:Yes	citation	CitationClass=web }}</ref>
Perl	Template:Yes	Larry Wall prefers 4 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>
PHP	Template:Yes	Drupal use 2 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> PEAR and Zend use 4 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> CodeIgniter and WordPress use tabs<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> PSR-2 specifies 4 spaces<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>
PowerShell	Template:Yes	citation	CitationClass=web }}</ref>
Python	Template:No	citation	CitationClass=web }}</ref>
Ruby	Template:Yes	citation	CitationClass=web }}</ref>
Rust	Template:Yes	citation	CitationClass=web }}</ref>
Scala	Template:Yes	citation	CitationClass=web }}</ref>
Swift	Template:Yes	citation	CitationClass=web }}</ref>
Tcl	Template:Yes	citation	CitationClass=web }}</ref>
Visual Basic	Template:Yes	citation	CitationClass=web }}</ref>
XML	Template:Yes	citation	CitationClass=web }}</ref>

Elastic tabstops

In 2006, a new method of indentation was proposed, called elastic tabstops.Template:Cn