Whitespace character explained

A whitespace character is a character data element that represents white space when text isrendered for display by a computer.

For example, a space character (ASCII 32) represents blank space such as a word divider in a Western script.

A printable character results in output when rendered,but a whitespace character does not.Instead, whitespace characters define the layout of text to a limited degree interrupting the normal sequence of rendering characters next to each other. The output of subsequent characters is typically shifted to the right (or to the left for right-to-left script) or to the start of the next line. The effect of multiple sequential whitespace characters is cumulative such that the next printable character is rendered in a location based on the accumulated effect of preceding whitespace characters.

The term whitespace is rooting in the common practice of rendering text on white paper. Normally, a whitespace character is not rendered as white. It affects rendering, but it is not itself rendered.

Overview

A space character typically inserts horizontal space that is about as wide as a letter. For a monospaced font the width is the width of a letter, and for a variable-width font the width is font-specific. Some fonts support multiple space characters that have different widths.

A tab character typically inserts horizontal space that is based on tab stops which vary by application.

A newline character sequence typically moves the render output location to the beginning of the next line. If one follows text, it does not actually result in whitespace. But, two sequential newline sequences between text blocks results in a blank line between the blocks. The height of the blank line varies by application.

Using whitespace characters to layout text is a convention. Applications sometimes render whitespace characters as visible markup so that a user can see what is normally not visible.

Typically, a user types a space character by pressing, a tab character by pressing and newline by pressing .

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.

Substitute images

Unicode also provides some visible characters that can be used to represent various whitespace characters, in contexts where a visible symbol must be displayed:

Unicode space-illustrating characters (visible)
Code Decimal Name BlockDisplayDescription
U+00B7 183 Middle dot Latin-1 Supplement · Interpunct
Named entity: ·
U+21A1 8609 Downwards two headed arrow ArrowsECMA-17 / ISO 2047 symbol for form feed (page break)
U+2261 8810 Identical to Mathematical
Operators
Amongst other uses, is the ECMA-17 / ISO 2047 symbol for line feed
U+237D 9085 Shouldered open box Miscellaneous TechnicalUsed to indicate a NBSP
U+23CE 9166 Return symbol Miscellaneous TechnicalSymbol for a return key, which enters a line break
U+2409 9225 Symbol for horizontal tabulation Control PicturesSubstitutes for a tab character
U+240A 9226 Symbol for line feed Control PicturesSubstitutes for a line feed
U+240B 9227 Symbol for vertical tabulation Control PicturesSubstitutes for a vertical tab (line tab)
U+240C 9228 Symbol for form feed Control PicturesSubstitutes for a form feed (page break)
U+240D 9229 Symbol for carriage return Control PicturesSubstitutes for a carriage return
U+2420 9248 Symbol for space Control PicturesSubstitutes for an ASCII space
U+2422 9250 Blank symbol Control Picturesaka "substitute blank",[2] used in BCDIC, EBCDIC, ASCII-1963[3] etc. as a symbol for the word separator
U+2423 9251 Open box Control PicturesUsed in block letter handwriting at least since the 1980s when it is necessary to explicitly indicate the number of space characters (e.g. when programming with pen and paper). Used in a textbook (published 1982, 1984, 1985, 1988 by Springer-Verlag) on Modula-2,[4] a programming language where space codes require explicit indication. Also used in the keypad[5] of the Texas Instruments' TI-8x series of graphing calculators.
Named entity: ␣
U+2424 9252 Symbol for newline Control PicturesSubstitutes for a line break
U+25B3 9651 White up-pointing triangle Geometric ShapesAmongst other uses, is the ECMA-17 / ISO 2047 symbol for the ASCII space
U+2A5B 10843 Logical Or with middle stem Supplemental
Mathematical
Operators
Amongst other uses, is the ECMA-17 / ISO 2047 symbol for vertical tab (line tab)
U+2AAA 10922 Smaller than Supplemental
Mathematical
Operators
Amongst other uses, is the ECMA-17 / ISO 2047 symbol for carriage return
U+2AAB 10923 Larger than Supplemental
Mathematical
Operators
Amongst other uses, is the ECMA-17 / ISO 2047 symbol for the tab character
U+3037 12343 Ideographic Telegraph Line Feed
Separator Symbol
CJK Symbols
and Punctuation
Graphic used for code 9999 in Chinese telegraph code, representing a line feed
  1. Web site: The Unicode Standard. Unicode Consortium.
  2. Book: Coded Character Sets, History and Development . The Systems Programming Series . Mackenzie . Charles E. . 1980 . 1 . . 978-0-201-14460-4 . 77-90165 . 41, 47, 52, 102–103, 117, 119, 130, 132, 141, 148, 150–151, 212, 424 . 2019-08-25 . https://web.archive.org/web/20160526172151/https://textfiles.meulie.net/bitsaved/Books/Mackenzie_CodedCharSets.pdf . May 26, 2016 . live . mdy-all .
  3. Web site: American Standard Code for Information Interchange, ASA X3.4-1963 . American Standards Association (ASA) . 1963-06-17 .
  4. Book: Wirth, Niklaus . Programming in Modula-2 . 1988 . 978-3-642-83567-4 . 10.1007/978-3-642-83565-0.
  5. Above the zero "0" or negative "(‒)" key.
Exact space

Non-space blanks

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.

Many of the Unicode space characters were created for compatibility with classic print typography.[12]

Even if digital typography has algorithmic kerning and justification, those space characters can be used to supplement the electronic formatting when needed.

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.[13] 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  , though not universally supported in browsers 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 in particular being the thinnest of horizontal whitespace characters.

Normal space versus hair and thin spaces (as rendered by your browser)
Normal space with em dashleft  -  right
Thin space with em dashleft - right
Hair space with em dashleft  -  right
No space with em dashleft - right

Computing applications

Programming languages

In most programming language syntax, whitespace characters can be used to separate tokens. For a free-form language, whitespace characters are ignored by code processors (i.e. compiler). Even when language syntax requires white space, often multiple whitespace characters are treated the same as a single. In an off-side rule language, indentation white space is syntactically significant. In the satirical and contrarian language called Whitespace, whitespace characters are the only significant characters and normal text is ignored.

Good use of white space in source code can group related logic and make the code easier to understand.Excessive use of whitespace, including at the end of a line where it provides no rendering behavior, is considered a nuisance.

Most languages only recognize whitespace characters that have an ASCII code. They disallow most or all of the Unicode codes listed above. The C language defines whitespace characters to be "space, horizontal tab, new-line, vertical tab, and form-feed".[14] 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.

Command-line parsing

Typical command-line parsers use the space character to delimit arguments. A value with an embedded space character is problematic since it causes the value to parse as multiple arguments. Typically, a parser allows for escaping the normal argument parsing by enclosing the text in quotes.

Consider that one wants to list the files in directory named "foo bar". This command instead lists the files matching either "foo" or "bar":

ls foo bar

This command correctly specifies a single argument:

ls "foo bar"

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.[15] 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.[16] 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 . 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".[2] It was used in BCDIC,[2] EBCDIC,[2] and ASCII-1963.[2]

See also

External links