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.

Template:Anchors For first-line indentation the first line of a paragraph is indented, Template:Unichar

A first-line indentation of 2 em:

Template:Lorem ipsum 

Template:Anchor For hanging indentation all but the first line of a paragraph is indented.

A hanging indentation of 2 em:

Template:Lorem ipsum

Template:Anchor For block indentation the entire paragraph is indented relative to the preceding paragraph.

A block indentation of 2 em on the left:

Template:Lorem ipsum

Block indentation on both sides is commonly used for a quotation, a block quotation, here shown with 2 em on the left and right but since it is not right-aligned, the empty space on the right varies based on line length:

Template:Lorem ipsum

Here's the same as the previous but justified (left and right aligned):

Template:Lorem ipsum

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>Template:Cite 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	Fritz Mehner's style guide suggests 2, 4, or 8 spaces and uses 2 in all examples<ref>Template:Cite web</ref> Google uses 2 spaces <ref>Template:Cite web </ref>
C	Template:Yes	The Linux kernel uses 1 tab<ref>Template:Cite web </ref><ref> Template:Cite web </ref> NASA uses 4 spaces.<ref>Template:Cite web</ref> Clinton Staley advocates 3 spaces<ref>Template:Cite web</ref>
C++	Template:Yes	WebKit recommends 4 spaces<ref>Template:Cite web</ref> Google uses 2 spaces<ref>[1] Template:Webarchive</ref>
C#	Template:Yes	Microsoft convention: 4 spaces<ref>Template:Cite web</ref>
CSS	Template:Yes	Drupal, GitHub, and Google use 2 spaces<ref>Template:Cite web</ref><ref>Template:Cite web</ref><ref name="google">Template:Cite web This is an HTML-rendered copy of the official version, which is maintained in XML format</ref><ref>Template:Cite web</ref> WordPress uses tabs<ref>Template:Cite web</ref>
Dart	Template:Yes	dart format uses 2 spaces
Delphi	Template:Yes	Delphi style guide: 2 spaces <ref>Template:Cite web</ref>
F#	Template:Yes	F# style guide: 4 spaces<ref>Template:Cite web</ref>
Go	Template:Yes	Effective Go: 1 tab <ref>Template:Cite web</ref>
Haskell	Template:No	Google uses 2 spaces<ref>Template:Cite web</ref>
HTML	Template:Yes	Google uses 2 spaces<ref name="google" /> HTML Tidy defaults to 2 spaces<ref>Template:Cite web</ref>
Java	Template:Yes	Oracle uses 4 spaces<ref>Template:Cite web</ref> Android uses 4 spaces<ref>Template:Cite web</ref> Most Eclipse IDE components use tabs
JavaScript	Template:Yes	Douglas Crockford advocates 4 spaces<ref>Template:Cite web</ref> GitHub and Google use 2 spaces<ref>Template:Cite web</ref><ref>Template:Cite web</ref> jQuery uses tabs<ref>Template:Cite web</ref> Firefox's built-in jsbeautifier defaults to 2 spaces prettyprinter in Google Chrome and Internet Explorer use 4 spaces
Julia	Template:Yes	Julia style guide: 4 spaces<ref>Template:Cite web</ref>
Kotlin	Template:Yes	Kotlin style guide: 4 spaces<ref>Template:Cite web</ref>
Lua	Template:Yes	Lua style guide: 2 spaces<ref>Template:Cite web</ref>
Perl	Template:Yes	Larry Wall prefers 4 spaces<ref>Template:Cite web</ref>
PHP	Template:Yes	Drupal use 2 spaces<ref>Template:Cite web</ref> PEAR and Zend use 4 spaces<ref>Template:Cite web</ref><ref>Template:Cite web</ref> CodeIgniter and WordPress use tabs<ref>Template:Cite web</ref><ref>Template:Cite web</ref> PSR-2 specifies 4 spaces<ref>Template:Cite web</ref>
PowerShell	Template:Yes	Unofficial PowerShell Best Practices and Style Guide: 4 spaces<ref>Template:Cite web</ref>
Python	Template:No	PEP 8: 4 spaces<ref>Template:Cite web</ref>
Ruby	Template:Yes	Ruby style guide: 2 spaces <ref>Template:Cite web</ref>
Rust	Template:Yes	Rust style guide: 4 spaces <ref>Template:Cite web</ref>
Scala	Template:Yes	Scala style guide: 2 spaces <ref>Template:Cite web</ref>
Swift	Template:Yes	Google uses 2 spaces<ref>Template:Cite web</ref>
Tcl	Template:Yes	Tcl style guide: 4 spaces <ref>Template:Cite web</ref>
Visual Basic	Template:Yes	Microsoft convention: 4 spaces <ref>Template:Cite web</ref>
XML	Template:Yes	Google uses 2 spaces<ref>Template:Cite web</ref>

Elastic tabstops

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