Whitespace character
In computer science, whitespace is any single character or series of characters that represents horizontal or vertical space in typography. When rendered, a whitespace character does not correspond to a visual mark, but typically does occupy an area on a page. For example, the common whitespace symbol " " (Unicode code point U+0020, decimal 32) represents a blank space, used as a word divider in Western scripts.
The term "whitespace" is based on the assumption that the background color used for rendered text is white.
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[edit] Definition and ambiguity
As is common in technical literature, the two words "white space" have found widespread usage as the single term "whitespace", especially when used as an adjective, as in "whitespace character". Some specifications refer to "white space" while others refer to "whitespace"; there is no difference between the terms, although exactly which characters are being referred to does vary from context to context. For example, the form feed character is "whitespace" in HTML, but is not "white space" in XML.
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 key (Enter key) may be considered whitespace as well.
[edit] Unicode
In Unicode (Unicode Character Database) the following 26 characters are defined as whitespace character:
| Whitespace[a] (Unicode character property WSpace=Y) | ||||
|---|---|---|---|---|
| Code point | Name | Script | General category | Remark |
| U+0009 | Common | Other, control | HT, Horizontal Tab | |
| U+000A | Common | Other, control | LF, Line feed | |
| U+000B | Common | Other, control | VT, Vertical Tab | |
| U+000C | Common | Other, control | FF, Form feed | |
| U+000D | Common | Other, control | CR, Carriage return | |
| U+0020 | space | Common | Separator, space | |
| U+0085 | Common | Other, control | NEL, Next line | |
| U+00A0 | no-break space | Common | Separator, space | |
| U+1680 | ogham space mark | Ogham | Separator, space | |
| U+180E | mongolian vowel separator | Mongolian | Separator, space | |
| U+2000 | en quad | Common | Separator, space | |
| U+2001 | em quad | Common | Separator, space | |
| U+2002 | en space | Common | Separator, space | |
| U+2003 | em space | Common | Separator, space | |
| U+2004 | three-per-em space | Common | Separator, space | |
| U+2005 | four-per-em space | Common | Separator, space | |
| U+2006 | six-per-em space | Common | Separator, space | |
| U+2007 | figure space | Common | Separator, space | |
| U+2008 | punctuation space | Common | Separator, space | |
| U+2009 | thin space | Common | Separator, space | |
| U+200A | hair space | Common | Separator, space | |
| U+2028 | line separator | Common | Separator, line | |
| U+2029 | paragraph separator | Common | Separator, paragraph | |
| U+202F | narrow no-break space | Common | Separator, space | |
| U+205F | medium mathematical space | Common | Separator, space | |
| U+3000 | ideographic space | Common | Separator, space | |
| a. ^ Unicode 6.0, Chapter 4.6 | ||||
Within the algorithm for Bidirectional writing, Unicode uses another definition of "Whitespace" (Bidirectional Character Type=WS). These Bidi-WS characters (18 out of the 26 listed in the table here) are "Neutral", they do not determine a writing direction, they just follow neighboring characters in this. The eight other characters listed here are also "Neutral", but have a different Bidi-type.
[edit] Usage
[edit] Programming Languages
Runs of whitespace (beyond a first whitespace character) occurring within source code written in computer programming languages are generally ignored; such languages are free-form. But, for example, in Haskell and Python, whitespace and indentation are used for syntactical purposes. And in Whitespace, whitespaces are the only valid characters for programming, while any other characters are ignored.
Still, for most programming languages, abundant use of whitespace, especially trailing whitespace at the end of lines, is considered a nuisance. However correct use of whitespace aids developers. It can make the code easier to read and help group related logic. In interpreted languages, parsing of unnecessary whitespace may affect the speed of execution. In markup languages like HTML, unnecessary whitespace increases the file size, and may so affect the speed of transfer over a network. 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.
The C language defines whitespace to be "... space, horizontal tab, new-line, vertical tab, and form-feed". The HTTP network protocol has very strict requirements about what type of whitespace can occur in the control structures (such as the header fields) and where it must and must not occur.
[edit] Literature
On some occasions, such as a textbook on the Modula-2 computer language published ca. 1985 by Springer-Verlag, it is necessary to explicitly show a symbol to indicate a space code. That book, at least, used the symbol ␣ (Unicode U+2423, decimal 9251, OPEN BOX) to show an explicit space code. (In case it doesn't render well in your web browser, it's much like a ] (a closing square bracket) although not as wide, rotated a quarter-turn clockwise and placed below the writing line. Some fonts render it too narrowly.)
The TI-8x series graphing calculators from Texas Instruments, at least the early models, use the same symbol to represent the space character in the keypad silkscreening, although on the calculators' display, this character appears as a blank space as on typical computer monitors.
[edit] 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".
[edit] See also
- Programming style
- Whitespace (programming language)
- Indent style
- Space (punctuation)
- Trim (programming)
