Indentation (typesetting)

In the written form of many languages, an indentation or indent is an empty space at the beginning of a line to signal the start of a new paragraph. Many computer languages have adopted this technique to designate "paragraphs" or other logical blocks in the program.

For example, the following lines are indented, using between one and six spaces:

 This paragraph is indented by 1 space.

   This paragraph is indented by 3 spaces.

      This paragraph is indented by 6 spaces.

In computer programming, the neologisms outdent, unindent and dedent are used to describe the reversal of the indentation process, realigning text with the page margin (or with previous, lesser, levels of indentation).

In right-to-left languages (e.g. Hebrew and Arabic), indentation is used just the same, but from the right margin of the paper, where the line begins.

Indentation in typesetting

There are three main types of indentation, illustrated below in relation to borders representing the page dimensions.

A first-line indentation indents the first line.
A first-line indentation of 2 em:
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. 
A hanging indentation indents the rest of the text while leaving the first line in place.
A hanging indentation of 2 em:
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
A block indentation indents the entire block of text.
A block indentation of 2 em on the left:
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
Indentation from both sides is commonly used for block quotations, here shown with 2 em on the left and right (which may amount to more on the right for certain lines, depending on word wrapping, if the text does not have justified alignment):
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
A justified-text example of a block quotation that has been block-indented from both sides by 3 em:
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Indentation in programming
Main article: Indent style

In computer programming languages, indentation is used to format program source code to improve readability. Indentation is generally only of use to programmers; compilers and interpreters rarely care how much whitespace is present in between programming statements. However, certain programming languages rely on the use of indentation to demarcate programming structure, often using a variation of the off-side rule. The Haskell, Occam, Python, and Ya programming languages rely on indentation in this way.

Debates over where to indent, whether to use spaces or tabs, and how many spaces to use are often hotly debated among programmers, leading some to classify indentation as akin to a religious war.[1] In 2006 a third method of indentation was proposed, called elastic tabstops.

In addition to general indentation of statements, different bracket indentation styles are commonly used.

LanguageIndentNote
BashvariesFritz Mehner's Style Guide[2] suggests 2, 4, or 8 spaces and uses 2 in all examples. Google uses 2 spaces.[3]
CvariesThe Linux kernel uses 1 tab.[4] NASA uses 4 spaces.[5]
C++variesGoogle uses 2 spaces.[6]
C#4 spacesPer Microsoft's C# Coding Conventions.[7]
CSSvariesDrupal, GitHub, and Google use 2 spaces.[8][9][10][11] WordPress uses tabs.[12]
Delphi2 spacesDefault in RAD Studio.
F#4 spacesAs per the F# style guide.[13]
Go1 tabPer "Effective Go".[14]
HaskellvariesGoogle uses 2 spaces.[15]
HTMLvariesGoogle uses 2 spaces.[10] HTML Tidy defaults to 2 spaces.[16]
JavavariesOracle uses 4 spaces.[17] Android uses 4 spaces.[18] Most Eclipse IDE components use tabs.
JavaScriptvariesDouglas Crockford advocates 4 spaces.[19] GitHub and Google uses 2 spaces.[20][21] jQuery uses tabs.[22] Firefox's built-in jsbeautifier defaults to 2 spaces. The built-in prettyprinter in Google Chrome and Internet Explorer uses 4 spaces.
Julia 4 spaces Per Julia style guide.[23]
Kotlin 4 spaces Per Kotlin style guide.[24]
Lua2 spacesPer Lua Style Guide.[25]
Perl4 spacesPer "perlstyle: Perl style guide".[26]
PHPvariesDrupal use 2 spaces.[27] PEAR and Zend use 4 spaces.[28][29] CodeIgniter and WordPress uses tabs.[30][31] PSR-2 specifies 4 spaces.[32]
Python4 spacesPer PEP-8.[33] (1 tab is also sometimes used, but 4 spaces is preferred.)
Ruby2 spacesPer Ruby Style Guide.[34]
Rust4 spacesPer Rust Style Guide.[35]
Scala2 spacesPer Scala style guide.[36]
Tcl4 spacesPer Tcl style guide.[37]
Visual Basic4 spacesPer Microsoft's Visual Basic Coding Conventions.[38]

References
  1. "Tabs versus Spaces: An Eternal Holy War". Jwz.org. 2007-01-05. Retrieved 2014-01-18.
  2. "Bash Style Guide and Coding Standard" (PDF). Lug.fh-swf.de.
  3. "Archived copy". Archived from the original on 2014-06-26. Retrieved 2014-06-23.CS1 maint: archived copy as title (link)
  4. "Archived copy". Archived from the original on 2015-02-14. Retrieved 2015-02-15.CS1 maint: archived copy as title (link)
  5. "C STYLE GUIDE" (PDF). Homepages.inf.ed.ac.uk. August 1994. Retrieved 3 September 2017.
  6. Archived 2014-10-06 at the Wayback Machine
  7. Bill Wagner. "C# Coding Conventions (C# Programming Guide)". Msdn.microsoft.com. Retrieved 3 September 2017.
  8. "CSS formatting guidelines". Drupal.org. Retrieved 2014-01-18.
  9. "CSS · Styleguide · GitHub". Github.com. Retrieved 2014-01-18.
  10. "Google HTML/CSS Style Guide". Google GitHub. Indentation. Archived from the original on 2016-03-13. Retrieved 2016-03-13. Indent by 2 spaces at a time. This is an HTML-rendered copy of the official version, which is maintained in XML format
  11. "styleguide: Style guides for Google-originated open-source projects". Github.com. 3 September 2017. Retrieved 3 September 2017.
  12. "WordPress › CSS Coding Standards « Make WordPress Core". Make.wordpress.org. Retrieved 2018-07-20.
  13. "F# code formatting guidelines". docs.microsoft.com. Retrieved 14 October 2020.
  14. "Effective Go - The Go Programming Language". golang.org. Retrieved 3 September 2017.
  15. "HaskellStyleGuide - ganeti - Style Guide for the Haskell code - Cluster-based virtualization management software - Google Project Hosting". Code.google.com. 2014-01-08. Archived from the original on June 27, 2013. Retrieved 2014-01-18.
  16. "HTML Tidy Configuration Options Quick Reference". Tidy.sourceforge.net. 2008-06-18. Retrieved 2014-01-18.
  17. "Code Conventions for the Java Programming Language: 4. Indentation". Oracle.com. Retrieved 2014-01-18.
  18. "Code Style Guidelines for Contributors | Android Developers". Source.android.com. Retrieved 2014-01-18.
  19. "Code Conventions for the JavaScript Programming Language". Javascript.crockford.com. 2006-11-13. Retrieved 2014-01-18.
  20. "JavaScript 路 Styleguide". Github.com. Archived from the original on 2013-08-15. Retrieved 2014-01-18.
  21. "JaveScript Style Rules". Google-styleguide.googlecode.com. Archived from the original on 2014-02-16. Retrieved 2014-02-18.
  22. jQuery Foundation - jquery.org. "JavaScript Style Guide | Contribute to jQuery". Contribute.jquery.org. Retrieved 2014-01-18.
  23. "Style Guide · The Julia Language". docs.julialang.org.
  24. "Coding Conventions - Kotlin Programming Language". Kotlin.
  25. "lua-users wiki: Lua Style Guide". lua-users.org. Retrieved 3 September 2017.
  26. Allen, Jon (JJ), ed. (2015-06-15). "perlstyle: Perl style guide". Perl 5 Version 22.0 Documentation. Perl Foundation. Retrieved 2016-03-13.
  27. "Coding standards". Drupal.org. Retrieved 2014-01-18.
  28. "Manual :: Indenting and Line Length". Pear.php.net. Retrieved 2014-01-18.
  29. "PHP Coding Standard (draft) - Contributors - Zend Framework Wiki". Framework.zend.com. Archived from the original on 2008-01-03. Retrieved 2014-01-18.
  30. "Style Guide : CodeIgniter User Guide". Ellislab.com. Retrieved 2014-01-18.
  31. "WordPress › PHP Coding Standards « Make WordPress Core". Make.wordpress.org. Retrieved 2014-01-18.
  32. "PHP : Coding Style Guide". Php-fig.org. Archived from the original on 2014-03-15. Retrieved 2014-02-18.
  33. "PEP 8 -- Style Guide for Python Code". Python.org. Retrieved 3 September 2017.
  34. Batsov, Bozhidar (3 September 2017). "ruby-style-guide: A community-driven Ruby coding style guide". Github.com. Retrieved 3 September 2017.
  35. "rust: A safe, concurrent, practical language". Github.com. 3 September 2017. Retrieved 3 September 2017.
  36. "Indentation - Scala Documentation". docs.scala-lang.org. Retrieved 3 September 2017.
  37. Ray Johnson. "Tcl Style Guide" (PDF). Tcl.tk. Retrieved 3 September 2017.
  38. "Structured Coding Conventions". msdn.microsoft.com. Retrieved 3 September 2017.
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