In computer science, whitespace is any character or series of whitespace characters that represent horizontal or vertical space in typography. When rendered, a whitespace character does not correspond to a visible mark, but typically does occupy an area on a page. For example, the common whitespace symbol U+0020 space (HTML:
), also ASCII 32, represents a blank space punctuation character in text, used as a word divider in Western scripts.
With many keyboard layouts, a horizontal whitespace character may be entered through the use of a spacebar. Horizontal whitespace may also be entered on many keyboards through the use of the Tab ↹ key, although the length of the space may vary. Vertical whitespace is a bit more varied as to how it is encoded, but the most obvious in typing is the ↵ Enter result which creates a 'newline' code sequence in applications programs. Older keyboards might instead say Return, abbreviating the typewriter keyboard meaning 'Carriage-Return' which generated an electromechanical return to the left stop (CR code in ASCII-hex &0D;) and a line feed or move to the next line (LF code in ASCII-hex &0A;); in some applications these were independently used to draw text cell based displays on monitors or for printing on tractor-guided printers—which might also contain reverse motions/positioning code sequences allowing yesterdays text base fancier displays. Many early computer games used such codes to draw a screen.
The term "whitespace" is based on the resulting appearance on ordinary paper. However they are coded inside an application, whitespace can be processed the same as any other character code and programs can do the proper action as defined for the context in which they occur.
- 1 Definition and ambiguity
- 2 Whitespace and digital typography
- 3 Computing applications
- 4 See also
- 5 References
- 6 External links
Definition and ambiguity
In Unicode (Unicode Character Database) the following 25 characters are defined as whitespace characters. (Depending on the browser and fonts used to view this table, not all spaces may display properly.)
|[a](Unicode character property WSpace=Y)Whitespace|
|Code point||Name||Decimal||Display inside "]["||Break||in IDN||Script||Block||General category||Remarks|
|000009U+0009||character tabulation||9||] [||Yes||No||Common||Basic Latin||Other, control||HT, Horizontal Tab|
|000010U+000A||line feed||10||n/a||Common||Basic Latin||Other, control||LF, Line feed|
|000011U+000B||line tabulation||11||n/a||Common||Basic Latin||Other, control||VT, Vertical Tab|
|000012U+000C||device control two||12||n/a||Common||Basic Latin||Other, control||FF, Form feed|
|000013U+000D||device control three||13||n/a||Common||Basic Latin||Other, control||CR, Carriage return|
|000032U+0020||space||32||] [||Yes||No||Common||Basic Latin||Separator, space||Most common (normal ASCII space)|
|000133U+0085||next line||133||n/a||Common||Latin-1 Supplement||Other, control||NEL, Next line|
|000160U+00A0||no-break space||160||] [||No||No||Common||Latin-1 Supplement||Separator, space||Non-breaking space: identical to U+0020, but not a point at which a line may be broken. HTML/XML:
|005760U+1680||ogham space mark||5760||] [||Yes||Yes||Ogham||Ogham||Separator, space||Used for interword separation in Ogham text. Normally a vertical line in vertical text or a horizontal line in horizontal text, but may also be a blank space in "stemless" fonts. Requires an Ogham font.|
|008192U+2000||en quad||8192||] [||Yes||No[b]||Common||General Punctuation||Separator, space||Width of one en. U+2002 is canonically equivalent to this character; U+2002 is preferred.|
|008193U+2001||em quad||8193||] [||Yes||No[b]||Common||General Punctuation||Separator, space||Also known as "mutton quad". Width of one em. U+2003 is canonically equivalent to this character; U+2003 is preferred.|
|008194U+2002||en space||8194||] [||Yes||No[b]||Common||General Punctuation||Separator, space||Also known as "nut". Width of one en. U+2000 En Quad is canonically equivalent to this character; U+2002 is preferred. HTML/XML:
|008195U+2003||em space||8195||] [||Yes||No[b]||Common||General Punctuation||Separator, space||Also known as "mutton". Width of one em. U+2001 Em Quad is canonically equivalent to this character; U+2003 is preferred. HTML/XML:
|008196U+2004||three-per-em space||8196||] [||Yes||No[b]||Common||General Punctuation||Separator, space||Also known as "thick space". One third of an em wide. HTML/XML:
|008197U+2005||four-per-em space||8197||] [||Yes||No[b]||Common||General Punctuation||Separator, space||Also known as "mid space". One fourth of an em wide. HTML/XML:
|008198U+2006||six-per-em space||8198||] [||Yes||No[b]||Common||General Punctuation||Separator, space||One sixth of an em wide. In computer typography sometimes equated to U+2009.|
|008199U+2007||figure space||8199||] [||No||No[b]||Common||General Punctuation||Separator, space||Figure space. In fonts with monospaced digits, equal to the width of one digit.|
|008200U+2008||punctuation space||8200||] [||Yes||No[b]||Common||General Punctuation||Separator, space||As wide as the narrow punctuation in a font, i.e. the advance width of the period or comma. HTML/XML:
|008201U+2009||thin space||8201||] [||Yes||No[b]||Common||General Punctuation||Separator, space||One fifth (sometimes one sixth) of an em wide. Recommended for use as a thousands separator for measures made with SI units. Unlike U+2002 to U+2008, its width may get adjusted in typesetting. HTML/XML:
|008202U+200A||hair space||8202||] [||Yes||No[b]||Common||General Punctuation||Separator, space||Thinner than a thin space. HTML/XML:
|008232U+2028||line separator||8232||n/a||Common||General Punctuation||Separator, line|
|008233U+2029||paragraph separator||8233||n/a||Common||General Punctuation||Separator, paragraph|
|008239U+202F||narrow no-break space||8239||] [||No||No[b]||Common||General Punctuation||Separator, space||Similar in function to U+00A0 No-Break Space. Introduced in Unicode 3.0 for Mongolian, to separate a suffix from the word stem without indicating a word boundary. When used with Mongolian, its width is usually one third of the normal space; in other context, its width resembles that of the Thin Space (U+2009) at least with some fonts. This character is also used in French before ":;?!»" and after "«".|
|008287U+205F||medium mathematical space||8287||] [||Yes||No[b]||Common||General Punctuation||Separator, space||MMSP. Used in mathematical formulae. Four-eighteenths of an em. In mathematical typography, the widths of spaces are usually given in integral multiples of an eighteenth of an em, and 4/18 em may be used in several situations, for example between the a and the + and between the + and the b in the expression a + b.|
|012288U+3000||ideographic space||12288||] [||Yes||No[b]||Common||CJK Symbols and Punctuation||Separator, space||As wide as a CJK character cell (fullwidth). Used (for example) in tai tou.|
|Code point||Name||Decimal||Display inside "]["||Break||in IDN||Script||Block||General category||Remarks|
|006158U+180E||mongolian vowel separator||6158||][||Yes||Yes||Mongolian||Mongolian||Other, Format||MVS. A narrow space character, used in Mongolian to cause the final two characters of a word to take on different shapes. It is no longer classified as space character (i.e. in Zs category) in Unicode 6.3.0 even though it was in previous versions of the standard.|
|008203U+200B||zero width space||8203||][||Yes||No[b]||?||General Punctuation||Other, Format||ZWSP, zero-width space. Used to indicate word boundaries to text processing systems when using scripts that do not use explicit spacing. It is similar to the soft hyphen, with the difference that the latter is used to indicate syllable boundaries, and should display a visible hyphen when the line breaks at it.|
|008204U+200C||zero-width non-joiner||8204||][||Yes||Yes||?||General Punctuation||Other, Format||ZWNJ, zero-width non-joiner. When placed between two characters that would otherwise be connected, a ZWNJ causes them to be printed in their final and initial forms, respectively. HTML/XML:
|008205U+200D||zero-width joiner||8205||][||Yes||Yes||?||General Punctuation||Other, Format||ZWJ, zero-width joiner. When placed between two characters that would otherwise not be connected, a ZWJ causes them to be printed in their connected forms. HTML/XML:
|008288U+2060||word joiner||8288||][||No||Yes||?||General Punctuation||Other, Format||WJ. Identical to U+200B, but not a point at which a line may be broken. Introduced in Unicode 3.2 to replace the deprecated "zero width no-break space" function of the U+FEFF character.|
|065279U+FEFF||zero-width non-breaking space||65279||][||No||Yes||?||Arabic Presentation Forms-B||Other, Format||Zero-width non-breaking space. Used primarily as a Byte Order Mark. Use as an indication of non-breaking is deprecated as of Unicode 3.2, see U+2060 instead.|
Within the algorithm for bidirectional writing, Unicode uses another definition of "whitespace" (Bidirectional Character Type=WS). These Bidi-WS characters (18 out of the 25 listed in the table here) are "neutral": they follow the writing direction of neighboring characters rather than determining their own. The eight other characters listed here are also "neutral", but have a different bidi-type.
Unicode also provides some visible characters to stand in for whitespace when necessary:
|U+00B7||183||Middle dot||Basic Latin||·||interpunct, used in text processors. HTML also:
|U+237D||9085||Shouldered open box||Miscellaneous Technical||⍽||used for NBSP|
|U+2420||9248||Symbol for space||Control Pictures||␠|
|U+2422||9250||Blank symbol||Control Pictures||␢|
|U+2423||9251||Open box||Control Pictures||␣||Used in a textbook on the Modula-2 computer language published ca. 1985 by Springer-Verlag, where it is necessary to explicitly indicate a space code. Also used in the keypad silkscreening of TI-8x series graphing calculators from Texas Instruments.|
- The Braille Patterns Unicode block contains U+2800 ⠀ braille pattern blank (HTML:
⠀), a Braille pattern with no dots raised. Some fonts display the character as a fixed-width blank, however the Unicode standard explicitly states that it does not act as a space.
Whitespace and digital typography
Text editors, word processors, and desktop publishing software differ in how they represent whitespace on the screen, and how they represent spaces at the ends of lines longer than the screen or column width. In some cases, spaces are shown simply as blank space; in other cases they may be represented by an interpunct or other symbols. Many different characters (described below) could be used to produce spaces, and non-character functions (such as margins and tab settings) can also affect whitespace.
Variable-width general-purpose space
In computer character encodings, there is a normal general-purpose space (Unicode character U+0020; 32 decimal) whose width will vary according to the design of the typeface. Typical values range from 1/5 em to 1/3 em (in digital typography an em is equal to the nominal size of the font, so for a 10-point font the space will probably be between 2 and 3.3 points). Sophisticated fonts may have differently sized spaces for bold, italic, and small-caps faces, and often compositors will manually adjust the width of the space depending on the size and prominence of the text.
In addition to this general-purpose space, it is possible to encode a space of a specific width. See the table below for a complete list.
Breaking and non-breaking spaces
By default, computer programs usually assume that, in text with word wrap enabled, a line break may as necessary be inserted at the position of a space. The non-breaking space, U+00A0 (160 decimal), named entity
is intended to render the same as a normal space but prevents line-wrapping at that position. Hard spaces (contrasted with "soft spaces") may be defined by some word processors and operating systems as either a non-breaking space, a non-combining/non-expanding space, or some other special character.
Hair spaces around dashes
In American typography, both en dashes and em dashes are set continuous with the text (as illustrated by use in The Chicago Manual of Style, 6.80, 6.83–86). However, an em dash can optionally be surrounded with a so-called hair space, U+200A (8202 decimal), or thin space, U+2009 (8201 decimal). The thin space can be written in HTML by using the named entity
and the hair space can be written using numeric character reference
. This space should be much thinner than a normal space, and is seldom used on its own.
|Normal space||left right|
|Normal space with em dash||left — right|
|Thin space with em dash||left — right|
|Hair space with em dash||left — right|
|No space with em dash||left—right|
In programming language syntax, spaces are frequently used to explicitly separate tokens. Runs of whitespace characters (beyond the first) occurring within source code written in computer programming languages (outside of strings and other quoted regions) are ignored by most languages; such languages are called free-form. In a few languages, including Haskell, occam, ABC, and Python, white space and indentation are used for syntactical purposes. In the satirical language called Whitespace, whitespace characters are the only valid characters for programming, while any other characters are ignored.
Still, for most programming languages, excessive use of white space, especially trailing white space at the end of lines, is considered a nuisance.[by whom?] However correct use of white space can make the code easier to read and help group related logic. In interpreted languages, parsing of unnecessary white space may affect the speed of execution.
The C language defines whitespace characters to be "... space, horizontal tab, new-line, vertical tab, and form-feed". The HTTP network protocol requires different types of white space to be used in different parts of the protocol, such as: only the space character in the status line, CRLF at the end of a line, and "linear white space" in header values.
Command line user interfaces
In commands processed by command processors, e.g., in scripts and typed in, the space character can cause problems as it has two possible functions: as part of a command or parameter, or as a parameter or name separator. Ambiguity can be prevented either by prohibiting embedded spaces, or by enclosing a name with embedded spaces between quote characters.
Some markup languages, such as SGML, preserve whitespace as written.
Web markup languages such as XML and HTML treat whitespace characters specially, including space characters, for programmers' convenience. One or more space characters read by conforming display-time processors of those markup languages are collapsed to 0 or 1 space, depending on their semantic context. For example, double (or more) spaces within text are collapsed to a single space, and spaces which appear on either side of the "
=" that separates an attribute name from its value have no effect on the interpretation of the document. Element end tags can contain trailing spaces, and empty-element tags in XML can contain spaces before the "
/>". In these languages, unnecessary whitespace increases the file size, and so may slow network transfers. On the other hand, unnecessary whitespace can also inconspicuously mark code, similar to, but less obvious than comments in code. This can be desirable to prove an infringement of license or copyright that was committed by copying and pasting.
In XML attribute values, sequences of whitespace characters are treated as a single space when the document is read by a parser. Whitespace in XML element content is not changed in this way by the parser, but an application receiving information from the parser may choose to apply similar rules to element content. An XML document author can use the
xml:space="preserve" attribute on an element to instruct the parser to discourage the downstream application from altering whitespace in that element's content.
In most HTML elements, a sequence of whitespace characters is treated as a single inter-word separator, which may manifest as a single space character when rendering text in a language that normally inserts such space between words. Conforming HTML renderers are required to apply a more literal treatment of whitespace within a few prescribed elements, such as the
pre tag and any element for which CSS has been used to apply
pre-like whitespace processing. In such elements, space characters will not be "collapsed" into inter-word separators.
In both XML and HTML, the non-breaking space character, along with other non-"standard" spaces, is not treated as collapsible "whitespace", so it is not subject to the rules above.
Such usage is similar to multiword file names written for operating systems and applications that are confused by embedded space codes—such file names instead use an underscore (_) as a word separator, as_in_this_phrase.
Another such symbol was U+2422 ␢ blank symbol. This was used in the early years of computer programming when writing on coding forms. Keypunch operators immediately recognized the symbol as an "explicit space".
- Programming style
- Whitespace (programming language)
- Indent style
- Space (punctuation)
- Zero-width space
- Trimming (computer programming)
- Regular expression#POSIX character classes: the white space character class
- Additional information about spaces: The Unicode Standard ver. 5.2.0 – section 6.2 table 6-2, and section 16.2 Line and Word Breaking
- "Character design standards – space characters". Character design standards. Microsoft. 1998–1999. Retrieved 2009-05-18.
- The Unicode Standard 5.0, printed edition, p.205
- ISO/IEC 10646-1:1993/FDAM 29:1999(E)
- "Writing Systems and Punctuation" (PDF). The Unicode Standard 7.0. Unicode Inc. 2014. Retrieved 2014-11-02.
- "General Punctuation" (PDF). The Unicode Standard 5.1. Unicode Inc. 1991–2008. Retrieved 2009-05-13.
- Sargent, Murray III (2006-08-29). "Unicode Nearly Plain Text Encoding of Mathematics (Version 2)". Unicode Technical Note #28. Unicode Inc. pp. 19–20. Retrieved 2009-05-19.
- Gillam, Richard (2002). Unicode Demystified: A Practical Programmer's Guide to the Encoding Standard. Addison-Wesley. ISBN 0-201-70052-2.
- "Network.IDN.blacklist chars". MozillaZine. 2009-02-24. Retrieved 18 September 2010.
- Above the zero "0" or negative "(‒)" key
- http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf Section 6.4, paragraph 3
- R. Fielding et al., "2.2 Basic Rules", Hypertext Transfer Protocol—HTTP/1.1, RFC 2616
- "3.3.3 Attribute-Value Normalization". Extensible Markup Language (XML) 1.0 (Fifth Edition). World Wide Web Consortium.
- "9.1 White space". W3CHTML 4.01 Specification. World Wide Web Consortium.