Whitespace character

In computer science, white space is any character or series of 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.

Overview

Relative widths of various spaces in Unicode.

With many keyboard layouts, a horizontal whitespace character may be entered through the use of a spacebar. Horizontal white space may also be entered on many keyboards through the use of the Tab ↹ key, although the length of the space may vary. Vertical white space 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 (e.g., Kingdom of Kroz^[1]).

The term "white space" is based on the resulting appearance on ordinary paper. However they are coded inside an application, white space 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.

Definition and ambiguity

The most common whitespace characters may be typed via the space bar or the tab key. Depending on context, a line-break generated by the return or enter key may be considered white space as well.

Unicode

The table below lists the twenty-five characters defined as whitespace ("WSpace=Y", "WS") characters in the Unicode Character Database.^[2] Seventeen use a definition of white space consistent with the algorithm for bidirectional writing ("Bidirectional Character Type=WS") and are known as "Bidi-WS" characters. The remaining characters may also be used, but are not of this "Bidi" type.

Note: Depending on the browser and fonts used to view the following table, not all spaces may be displayed properly.

Whitespace
(Unicode character property "WSpace=Y") ^{[lower-alpha 1]}

Code point	Name	Decimal	within "]["	Wrap- pable?	in IDN?	Script	Block	General category	Notes
000009U+0009	character tabulation	9	] [	Yes	No	Common	Basic Latin	Other, control	HT, Horizontal Tab. HTML/XML named entity: `&Tab;`, LaTeX: '\tab'
000010U+000A	line feed	10				Common	Basic Latin	Other, control	LF, Line feed. HTML/XML named entity: `&NewLine;`
000011U+000B	line tabulation	11				Common	Basic Latin	Other, control	VT, Vertical Tab
000012U+000C	form feed	12				Common	Basic Latin	Other, control	FF, Form feed
000013U+000D	carriage return	13				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				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 named entity: ` `, LaTeX: '\ '
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^{[lower-alpha 2]}	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^{[lower-alpha 2]}	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^{[lower-alpha 2]}	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 named entity: `&ensp;`, LaTeX: '\enspace'
008195U+2003	em space	8195	] [	Yes	No^{[lower-alpha 2]}	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 named entity: `&emsp;`, LaTeX: '\quad'
008196U+2004	three-per-em space	8196	] [	Yes	No^{[lower-alpha 2]}	Common	General Punctuation	Separator, space	Also known as "thick space". One third of an em wide. HTML/XML named entity: `&emsp13;`
008197U+2005	four-per-em space	8197	] [	Yes	No^{[lower-alpha 2]}	Common	General Punctuation	Separator, space	Also known as "mid space". One fourth of an em wide. HTML/XML named entity: `&emsp14;`
008198U+2006	six-per-em space	8198	] [	Yes	No^{[lower-alpha 2]}	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^{[lower-alpha 2]}	Common	General Punctuation	Separator, space	Figure space. In fonts with monospaced digits, equal to the width of one digit. HTML/XML named entity: `&numsp;`
008200U+2008	punctuation space	8200	] [	Yes	No^{[lower-alpha 2]}	Common	General Punctuation	Separator, space	As wide as the narrow punctuation in a font, i.e. the advance width of the period or comma.^[3] HTML/XML named entity: `&puncsp;`
008201U+2009	thin space	8201	] [	Yes	No^{[lower-alpha 2]}	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.^[4] HTML/XML named entity: ` `; Latex: '\,'
008202U+200A	hair space	8202	] [	Yes	No^{[lower-alpha 2]}	Common	General Punctuation	Separator, space	Thinner than a thin space. HTML/XML named entity: `&hairsp;`
008232U+2028	line separator	8232				Common	General Punctuation	Separator, line
008233U+2029	paragraph separator	8233				Common	General Punctuation	Separator, paragraph
008239U+202F	narrow no-break space	8239	] [	No	No^{[lower-alpha 2]}	Common	General Punctuation	Separator, space	Narrow no-break space. Similar in function to U+00A0 No-Break Space. When used with Mongolian, its width is usually one third of the normal space; in other context, its width sometimes resembles that of the Thin Space (U+2009).
008287U+205F	medium mathematical space	8287	] [	Yes	No^{[lower-alpha 2]}	Common	General Punctuation	Separator, space	MMSP. Used in mathematical formulae. Four-eighteenths of an em.^[5] 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.^[6] HTML/XML named entity:
012288U+3000	ideographic space	12288	]　[	Yes	No^{[lower-alpha 2]}	Common	CJK Symbols and Punctuation	Separator, space	As wide as a CJK character cell (fullwidth). Used, for example, in tai tou.

Related characters
Code point	Name	Decimal	within "]["	Wrap- pable?	in IDN?	Script	Block	General category	Notes
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.^[7] 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^{[lower-alpha 2]}	?	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. HTML/XML named entity: `&NegativeMediumSpace;`
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 named entity: `&zwnj;`
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 named entity: `&zwj;`
008288U+2060	word joiner	8288	]⁠[	No	Yes	?	General Punctuation	Other, Format	WJ, word joiner. Similar to U+200B, but not a point at which a line may be broken. HTML/XML named entity: `&NoBreak;`
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.

↑ Unicode 8.0 property list 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 This character is blacklisted for domain names by browsers because it might be used for phishing.^[8]

Substitutes

Unicode also provides some visible characters that can be used to represent white space:

Unicode space-illustrating characters (visible)
Code	Decimal	Name	Block	Display	Description
U+00B7	183	Middle dot	Basic Latin	·	Interpunct Named entity: `·`
U+237D	9085	Shouldered open box	Miscellaneous Technical	⍽	Used to indicate a 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 (published c. 1985 by Springer-Verlag) on Modula-2, a programming language where space codes require explicit indication. Also used in the keypad silkscreening^{[n 1]} of the Texas Instruments' TI-8x series of graphing calculators. Named entity: `&blank;`

Non-space blanks

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

On-screen display

Text editors, word processors, and desktop publishing software differ in how they represent white space 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 white space.

Variable-width general-purpose space

In computer character encodings, there is a normal general-purpose space (Unicode character U+0020) 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, 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, em dashes used as parenthetical dividers, and en dashes when used as word joiners, are set continuous with the text (as illustrated by use in The Chicago Manual of Style, 6.80, 6.83–86). However, such a dash can optionally be surrounded with a hair space, U+200A, or thin space, U+2009. The hair space can be written in HTML by using the numeric character references   or  . The thin space is named entity   and numeric references   or  . These spaces are much thinner than a normal space (except in a monospaced (non-proportional) font), with the hair space being the thinner of the two.

Normal space versus hair and thin spaces
(as rendered by your browser)
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

Computing applications

Programming languages

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. 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 white space characters to be "... space, horizontal tab, new-line, vertical tab, and form-feed".^[9] 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.^[10]

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.

Markup languages

Some markup languages, such as SGML, preserve white space 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 white space increases the file size, and so may slow network transfers. On the other hand, unnecessary white space 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.^[11] White space 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 white space 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.^[12] Conforming HTML renderers are required to apply a more literal treatment of white space 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 "white space", so it is not subject to the rules above.

File names

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".

Notes

↑ Above the zero "0" or negative "(‒)" key.

References

↑ "Kroz series".
↑ "The Unicode Standard". Unicode Consortium.
↑ "Character design standards – space characters". Character design standards. Microsoft. 1998–1999. Retrieved 2009-05-18.
↑ The Unicode Standard 5.0, printed edition, p.205
↑ "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.
↑ 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.

External links

Propertylist of Unicode Character Database

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