In writing, a space ( ) is a blank area devoid of content, serving to separate words, letters, numbers, and punctuation. Conventions for interword and intersentence spaces vary among languages, and in some cases the spacing rules are quite complex.

Latin was originally written scripta continua, without any word separators. There was a brief use of interpuncts (centred dots) to make reading Latin easier, but that practice was abandoned sometime around the year 200 CE. In around 600–800 CE, blank spaces started being inserted between words in Latin, and that practice carried over to all languages using the Latin alphabet (e.g. English). In typesetting, spaces have historically been of multiple lengths with particular space-lengths being used for specific typographic purposes, such as separating words or separating sentences or separating punctuation from words. Following the invention of the typewriter and the subsequent overlap of designer style-preferences and computer-technology limitations, much of this reader-centric variation has been lost in normal use.

In computer representation of text, spaces of various sizes, styles, or language characteristics (different space characters) are indicated with unique code points.

[edit] Use of the space in natural languages

[edit] Spaces between words

Modern English uses a space to separate words, but not all languages follow this practice. Spaces were not used to separate words in Latin until roughly AD 600–AD 800. Ancient Hebrew and Arabic did use spaces, partly to compensate in clarity for the lack of vowels. Traditionally, all CJK languages have no spaces: modern Chinese and Japanese (except when written with little or no kanji) still do not, but modern Korean uses spaces.

[edit] Spaces between sentences

There are three main conventions relating to the number of spaces used to separate sentences within the same paragraph:

• one widened space, typically two to three times wider than an inter-word space (traditional typography)
• two normal-width spaces (double spacing, English spacing or American typewriter spacing)
• one normal-width space (French spacing)

"Double spacing" can also refer to a style of line spacing: the insertion of a full additional empty line between lines of text. This is commonly used for text which may incorporate later markup or modifications, such as proof-readers' copies, legal documents, or academic assignments for correction.

[edit] Spaces and unit symbols

In Canadian Style: A Guide to Writing and Editing:

• When symbols are used, the prefix symbol and unit symbols are run together:

5 cm

7 hL

4 dag

13 kPa

• When a symbol consists entirely of letters, leave a full space between the quantity and the symbol:

45 kg not 45kg

• When the symbol includes a non-letter character as well as letter, leave no space:

32°C not 32° C or 32 °C

• For the sake of clarity, a hyphen may be inserted between a numeral and a symbol used adjectivally:

35-mm film

60-W bulb

[edit] Space characters and digital typography

[edit] The 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.

(In monospaced proofreading copy, only em- and en-spaces are represented using this character (which is called an em-quad or an en-quad), while other types of spaces are represented with a number sign.

[edit] Breaking and non-breaking spaces

By default, computer programs usually assume that, in flowing text, a line break may as necessary be inserted at the position of a space. The non-breaking space, U+00A0 (160 decimal), renders the same as a normal space but prevents line-wrapping at that position.

The generic Unicode space is often^{[citation needed]} considered insignificant when appearing at the end of a line of text, or when part of a sequence of whitespace characters, so it may be omitted or "collapsed" in such circumstances. The non-breaking space is expressly non-collapsible and may be used to indent text, though best World Wide Web practice prescribes using CSS for this purpose.

[edit] 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). This space should be much thinner than a normal space, and is seldom used on its own. It can be written in HTML by using the numeric character reference   or  . Very few user agents are able to render a hair space correctly:^{[citation needed]} in most cases the result is an unwanted symbol or a question mark on the screen, depending on the font and renderer capabilities.

[edit] Table of spaces

Unicode defines several space characters with specific semantics and rendering characteristics, as shown in the table below. Depending on the browser and fonts used to view this table, not all spaces may display properly:

Unicode also provides some visible characters to stand in for space when necessary in the "Control Pictures" block: the Symbol For Space ␠ (U+2420), the Blank Symbol ␢ (U+2422), and the Open Box ␣ (U+2423). The interpunct · is also often used to represent a space in word processing programs such as Microsoft Word.

[edit] Use of the space in computing

In programming language syntax, spaces are frequently used to explicitly separate tokens. Aside from this use, spaces and other whitespace characters are usually ignored by modern programming languages. Exceptions are Haskell, occam, ABC, and Python, which use the amount of whitespace in indentation to indicate the bounds of a block, and a whimsical language called Whitespace, where whitespace is the only meaningful syntactical element.

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.

[edit] Space characters in markup languages

Generalised markup languages, such as SGML, do not treat space characters differently from other characters.

However, special-purpose markup languages may do. In particular, 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 XML attribute values, sequences of whitespace characters are treated as a single space when the document is read by a parser.^[7] 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 force 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.^[8] 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.

[edit] See also

• Hard space
• Hyphenation
• Internal field separator
• Non-breaking space

[edit] References

1. ^ Gillam, Richard (2002). Unicode Demystified: A Practical Programmer's Guide to the Encoding Standard. Addison-Wesley. ISBN 0-201-70052-2. 
2. ^ "Character design standards - space characters". Character design standards. Microsoft. 1998–1999. http://www.microsoft.com/typography/developers/fdsspec/spaces.htm. Retrieved 2009-05-18. 
3. ^ The Unicode Standard 5.0, printed edition, p.205
4. ^ ISO/IEC 10646-1:1993/FDAM 29:1999(E)
5. ^ "General Punctuation" (PDF). The Unicode Standard 5.1. Unicode Inc. 1991–2008. http://www.unicode.org/charts/PDF/U2000.pdf. Retrieved 2009-05-13. 
6. ^ Sargent, Murray III (2006-08-29). "Unicode Nearly Plain Text Encoding of Mathematics (Version 2)". Unicode Technical Note #28. Unicode Inc. pp. 19–20. http://www.unicode.org/notes/tn28/tn28-2.html. Retrieved 2009-05-19. 
7. ^ http://www.w3.org/TR/REC-xml/#AVNormalize
8. ^ http://www.w3.org/TR/html4/struct/text.html#h-9.1

[edit] External links

• Unicode spaces, by Jukka "Yucca" Korpela.
• Commonly confused characters