Whitespace (computer Science)

In computer programming, whitespace 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   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 . Horizontal whitespace may also be entered on many keyboards through the use of the 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 result which creates a 'newline' code sequence in applications programs. Older keyboards might instead say , 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 text-based output devices to achieve more sophisticated output. Many early computer games used such codes to draw a screen (e.g. Kingdom of Kroz), and word processing software would use this to produce printed effects such as bold, underline, and strikeout.

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.

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 whitespace as well.

Unicode

The table below lists the twenty-five characters defined as whitespace ("WSpace=Y", "WS") characters in the Unicode Character Database.[1] Seventeen use a definition of whitespace 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.

Unicode character property "WSpace=Y"[a]
Code point  Name  Decimal  within "]["   Wrap-
  pable
in IDN  Script   Block  General
 category
 Notes 
U+0009 character tabulation 9 ] [ Yes No Common Basic Latin Other,
control
HT, Horizontal Tab. HTML/XML named entity: 	, LaTeX: '\tab'
U+000A line feed 10 Is a line-break Common Basic Latin Other,
control
LF, Line feed. HTML/XML named entity: 

U+000B line tabulation 11 Is a line-break Common Basic Latin Other,
control
VT, Vertical Tab
U+000C form feed 12 Is a line-break Common Basic Latin Other,
control
FF, Form feed
U+000D carriage return 13 Is a line-break Common Basic Latin Other,
control
CR, Carriage return
U+0020 space 32 ] [ Yes No Common Basic Latin Separator,
space
Most common (normal ASCII space)
U+0085 next line 133 Is a line-break Common Latin-1
Supplement
Other,
control
NEL, Next line
U+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:
U+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.
U+2000 en quad 8192 ] [ Yes Permitted, but displayed as Punycode in practice[b] Common General
Punctuation
Separator,
space
Width of one en. U+2002 is canonically equivalent to this character; U+2002 is preferred.
U+2001 em quad 8193 ] [ Yes Permitted, but displayed as Punycode in practice[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.
U+2002 en space 8194 ] [ Yes Permitted, but displayed as Punycode in practice[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 named entity:  , LaTeX: '\enspace'
U+2003 em space 8195 ] [ Yes Permitted, but displayed as Punycode in practice[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 named entity:  , LaTeX: '\quad'
U+2004 three-per-em space 8196 ] [ Yes Permitted, but displayed as Punycode in practice[b] Common General
Punctuation
Separator,
space
Also known as "thick space". One third of an em wide. HTML/XML named entity:  
U+2005 four-per-em space 8197 ] [ Yes Permitted, but displayed as Punycode in practice[b] Common General
Punctuation
Separator,
space
Also known as "mid space". One fourth of an em wide. HTML/XML named entity:  
U+2006 six-per-em space 8198 ] [ Yes Permitted, but displayed as Punycode in practice[b] Common General
Punctuation
Separator,
space
One sixth of an em wide. In computer typography, sometimes equated to U+2009.
U+2007 figure space 8199 ] [ No Permitted, but displayed as Punycode in practice[b] Common General
Punctuation
Separator,
space
Figure space. In fonts with monospaced digits, equal to the width of one digit. HTML/XML named entity:  
U+2008 punctuation space 8200 ] [ Yes Permitted, but displayed as Punycode in practice[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.[2] HTML/XML named entity:  
U+2009 thin space 8201 ] [ Yes Permitted, but displayed as Punycode in practice[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.[3] HTML/XML named entity:  ; LaTeX: '\,'
U+200A hair space 8202 ] [ Yes Permitted, but displayed as Punycode in practice[b] Common General
Punctuation
Separator,
space
Thinner than a thin space. HTML/XML named entity:  
U+2028 line separator 8232 Is a line-break Common General
Punctuation
Separator,
line
U+2029 paragraph separator 8233 Is a line-break Common General
Punctuation
Separator,
paragraph
U+202F narrow no-break space 8239 ] [ No Permitted, but displayed as Punycode in practice[b] 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).
U+205F medium mathematical space 8287 ] [ Yes Permitted, but displayed as Punycode in practice[b] Common General
Punctuation
Separator,
space
MMSP. Used in mathematical formulae. Four-eighteenths of an em.[4] 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.[5] HTML/XML named entity:  
U+3000 ideographic space 12288 ] [ Yes Permitted, but displayed as Punycode in practice[b] Common CJK Symbols
and
Punctuation
Separator,
space
As wide as a CJK character cell (fullwidth). Used, for example, in tai tou.
Related whitespace characters without Unicode character property "WSpace=Y"
Code point  Name  Decimal  within "]["   Wrap-
  pable
 in IDN  Script   Block  General
 category
 Notes 
U+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.[6] 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.
U+200B zero width space 8203 ]​[ Yes Permitted, but displayed as Punycode in practice[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. HTML/XML named entity: ​
U+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: ‌
U+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: ‍
U+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: ⁠
U+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.
  1. ^ "Unicode 11.0 UCD: PropList.txt". 2018-03-15. Retrieved . 
  2. ^ a b c d e f g h i j k l m n o This character is blacklisted for domain names by browsers because it might be used for phishing.[7]


Substitutes

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

  1. ^ Above the zero "0" or negative "(-)" key.
Non-space blanks
  • The Braille Patterns Unicode block contains 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.
Exact space
  • The Cambridge Z88 provided a special "exact space" (code point 160 aka 0xA0) (invokable by key shortcut +,[13]) displayed as "..." by the operating system's display driver.[14][15] It was therefore also known as "dot space" in conjunction with BBC BASIC.[14][15]
  • Under code point 224 (0xE0) the computer also provided a special three-character-cells-wide SPACE symbol "SPC" (analogous to Unicode's single-cell-wide U+2420).[14][15]

Whitespace and digital typography

On-screen display

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) 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.

Hair spaces around dashes

Em dashes used as parenthetical dividers, and en dashes when used as word joiners, are usually set continuous with the text.[16] 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  , or the named entity  , but is not universally supported in browsers yet, as of 2016.[which?] 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

Formatting values of quantities

The International System of Units (SI) prescribes inserting a space between a number and a unit of measurement and between units in compound units. A thin space should be used as thousands separator. See unit symbols and numbers.

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, whitespace 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 whitespace, especially trailing whitespace at the end of lines, is considered a nuisance. However correct use of whitespace can make the code easier to read and help group related logic.

The C language defines whitespace characters to be "space, horizontal tab, new-line, vertical tab, and form-feed".[17] The HTTP network protocol requires different types of whitespace 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 whitespace" in header values.[18]

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 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.[19] 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.[20] 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.

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 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".[10] It was used in BCDIC,[10]EBCDIC,[10] and ASCII-1963.[10]

See also

References

  1. ^ "The Unicode Standard". Unicode Consortium. 
  2. ^ "Character design standards - space characters". Character design standards. Microsoft. 1998-1999. Archived from the original on August 23, 2000. Retrieved . 
  3. ^ The Unicode Standard 5.0, printed edition, p.205
  4. ^ "General Punctuation" (PDF). The Unicode Standard 5.1. Unicode Inc. 1991-2008. Retrieved . 
  5. ^ 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 . 
  6. ^ Gillam, Richard (2002). Unicode Demystified: A Practical Programmer's Guide to the Encoding Standard. Addison-Wesley. ISBN 0-201-70052-2. 
  7. ^ "Network.IDN.blacklist chars". MozillaZine. 2009-02-24. Retrieved 2010. 
  8. ^ a b c d e f g h Mackenzie, Charles E. (1980). Coded Character Sets, History and Development. The Systems Programming Series (1 ed.). Addison-Wesley Publishing Company, Inc. pp. 41, 47, 52, 102-103, 117, 119, 130, 132, 141, 148, 150-151, 212, 424. ISBN 0-201-14460-3. LCCN 77-90165. Retrieved .  [1]
  9. ^ "American Standard Code for Information Interchange, ASA X3.4-1963". American Standards Association (ASA). 1963-06-17. Archived from the original on 2016-05-26. Retrieved . 
  10. ^ Niklaus Wirth, Programming in Modula-2
  11. ^ "Cambridge Z88 User Guide". 4.7 (4th ed.). Cambridge Computer Limited. 2016 [1987]. Basic concepts - The keyboard. Archived from the original on 2016-12-12. Retrieved . 
  12. ^ a b c "Cambridge Z88 User Guide". 4.0 (4th ed.). Cambridge Computer Limited. 1987. Appendix D. Archived from the original on 2016-12-12. Retrieved . 
  13. ^ a b c "Cambridge Z88 User Guide". 4.7 (4th ed.). Cambridge Computer Limited. 2015 [1987]. Appendix D. Archived from the original on 2016-12-12. Retrieved . 
  14. ^ Usage of the different dash types is illustrated, e.g., in The Chicago Manual of Style, §§ 6.80, 6.83-6.86
  15. ^ http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf Section 6.4, paragraph 3
  16. ^ R. Fielding et al., "2.2 Basic Rules", Hypertext Transfer Protocol--HTTP/1.1, RFC 2616Freely accessible 
  17. ^ "3.3.3 Attribute-Value Normalization". Extensible Markup Language (XML) 1.0 (Fifth Edition). World Wide Web Consortium. 
  18. ^ "9.1 Whitespace". W3CHTML 4.01 Specification. World Wide Web Consortium. 

External links


  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.

Whitespace_(computer_science)
 



 

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