Whitespace character

A whitespace character is a character data element that represents space |white space] when text is
rendered for display by a computer.
For example, a space character 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 start of the next line.
The effect of multiple sequential whitespace characters is cumulative such that the next printable character is rendered at a location based on the accumulated effect of preceding whitespace characters.
The origin of the term whitespace is rooted 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 lay out 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 characters in the Unicode Character Database. Seventeen use a definition of whitespace consistent with the algorithm for bidirectional writing 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:

Code	Decimal	Name	Block	Display	Description
U+00B7	183	Middle dot	Latin-1 Supplement	·	Interpunct Named entity: `·`
U+21A1	8609	Downwards two headed arrow	Arrows	↡	ECMA-17 / ISO 2047 symbol for form feed
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 Technical	⍽	Used to indicate a NBSP
U+23CE	9166	Return symbol	Miscellaneous Technical	⏎	Symbol for a return key, which enters a line break
U+2409	9225	Symbol for horizontal tabulation	Control Pictures	␉	Substitutes for a tab character
U+240A	9226	Symbol for line feed	Control Pictures	␊	Substitutes for a line feed
U+240B	9227	Symbol for vertical tabulation	Control Pictures	␋	Substitutes for a vertical tab
U+240C	9228	Symbol for form feed	Control Pictures	␌	Substitutes for a form feed
U+240D	9229	Symbol for carriage return	Control Pictures	␍	Substitutes for a carriage return
U+2420	9248	Symbol for space	Control Pictures	␠	Substitutes for an ASCII space
U+2422	9250	Blank symbol	Control Pictures	␢	aka "substitute blank", used in BCDIC, EBCDIC, ASCII-1963 etc. as a symbol for the word separator
U+2423	9251	Open box	Control Pictures	␣	Used in block letter handwriting at least since the 1980s when it is necessary to explicitly indicate the number of space characters. Used in a textbook on Modula-2, a programming language where space codes require explicit indication. Also used in the keypad of the Texas Instruments' TI-8x series of graphing calculators. Named entity: `&blank;`
U+2424	9252	Symbol for newline	Control Pictures	␤	Substitutes for a line break
U+25B3	9651	White up-pointing triangle	Geometric Shapes	△	Amongst 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
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+2B1A	11034	Dotted square	Miscellaneous Symbols and Arrows	⬚
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

; Exact space

The Cambridge Z88 provided a special "exact space" , displayed as "…" by the operating system's display driver. It was therefore also known as "dot space" in conjunction with BBC BASIC.
Under code point 224 the computer also provided a special three-character-cells-wide SPACE symbol "SPC".
Non-space blanks
The Braille Patterns Unicode block contains, 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.
Unicode's coverage of the Korean alphabet includes several code points which represent the absence of a written letter, and thus do not display a glyph:
* Unicode includes a Hangul Filler character in the Hangul Compatibility Jamo block. This is classified as a letter, but displayed as an empty space, like a Hangul block containing no jamo. It is used in KS X 1001 Hangul combining sequences to introduce them or denote the absence of a letter in a position, but not in Unicode's combining jamo system.
* Unicode's combining jamo system uses similar Hangul Choseong Filler and Hangul Jungseong Filler characters to denote the absence of a letter in initial or medial position within a syllable block, which are included in the Hangul Jamo block.
* Additionally, a Halfwidth Hangul Filler is included in the Halfwidth and Fullwidth Forms, which is used when mapping from encodings which include characters from both Johab and N-byte Hangul, such as IBM-933, which includes both Johab and EBCDIC fillers.
Whitespace and digital typography

On-screen display

s, 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 could be used to produce spaces, and non-character functions can also affect whitespace.
Many of the Unicode space characters were created for compatibility with classic print typography.
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 whose width will vary according to the design of the typeface. Typical values range from 1/5 em to 1/3 em. 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 above for a complete list.

Hair spaces around dashes

es used as parenthetical dividers, and en dashes when used as word joiners, are usually set continuous with the text. 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 &hairsp;. The thin space is named entity   and numeric references   or  . These spaces are much thinner than a normal space, with the hair space in particular being the thinnest of horizontal whitespace characters.

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 most programming language syntax, whitespace characters can be used to separate tokens. For a free-form language, whitespace characters are ignored by code processors. 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". 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"

An alternative is to escape the space with a backslash:

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 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.

Preserving whitespace

In XML attribute values, sequences of whitespace characters are treated as a single space when the document is read by a parser. 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. Conforming HTML renderers apply literal whitespace behaviour to certain elements: those inside tags, and those where CSS property white-space is set to or. In these elements, space characters will not be "collapsed" into inter-word separators.
In MediaWiki markup, as well as the there is an optional tag, which also preserves whitespace. It requires Extension:Poem.
In both XML and HTML, the non-breaking space character, along with other "non-standard" spaces, is not treated as collapsible whitespace.

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