Whitespace character


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 represents a blank space punctuation character in text, used as a word divider in Western scripts.

Overview

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 and a line feed or move to the next line ; 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, 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 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.

Substitutes

Unicode also provides some visible characters that can be used to represent various whitespace characters, in contexts where a visible symbol must be displayed:
CodeDecimalNameBlockDisplayDescription
U+00B7183Middle dotLatin-1 Supplement · Interpunct
Named entity: ·
U+21A18609Downwards two headed arrowArrows ↡ ECMA-17 / ISO 2047 symbol for form feed
U+22618810Identical toMathematical
Operators		 ≡ Amongst other uses, is the ECMA-17 / ISO 2047 symbol for line feed
U+237D9085Shouldered open boxMiscellaneous Technical ⍽ Used to indicate a NBSP
U+23CE9166Return symbolMiscellaneous Technical ⏎ Symbol for a return key, which enters a line break
U+24099225Symbol for horizontal tabulationControl Pictures ␉ Substitutes for a tab character
U+240A9226Symbol for line feedControl Pictures ␊ Substitutes for a line feed
U+240B9227Symbol for vertical tabulationControl Pictures ␋ Substitutes for a vertical tab
U+240C9228Symbol for form feedControl Pictures ␌ Substitutes for a form feed
U+240D9229Symbol for carriage returnControl Pictures ␍ Substitutes for a carriage return
U+24209248Symbol for spaceControl Pictures ␠ Substitutes for an ASCII space
U+24229250Blank symbolControl Pictures ␢ aka "substitute blank", used in BCDIC, EBCDIC, ASCII-1963 etc. as a symbol for the word separator
U+24239251Open boxControl 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: ␣
U+24249252Symbol for newlineControl Pictures ␤ Substitutes for a line break
U+25B39651White up-pointing triangleGeometric Shapes △ Amongst other uses, is the ECMA-17 / ISO 2047 symbol for the ASCII space
U+2A5B10843Logical Or with middle stemSupplemental
Mathematical
Operators		 ⩛ Amongst other uses, is the ECMA-17 / ISO 2047 symbol for vertical tab
U+2AAA10922Smaller thanSupplemental
Mathematical
Operators		 ⪪ Amongst other uses, is the ECMA-17 / ISO 2047 symbol for carriage return
U+2AAB10923Larger thanSupplemental
Mathematical
Operators		 ⪫ Amongst other uses, is the ECMA-17 / ISO 2047 symbol for the tab character

; Exact space

On-screen display

, 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.

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 below 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  , but is not universally supported in browsers yet, as of 2016 The thin space is named entity   and numeric references   or  . These spaces are much thinner than a normal space, with the hair space being the thinner of the two.
Normal space with em dashleft — right
Thin space with em dashleft — right
Hair space with em dashleft — right
No space with em dashleft—right

Formatting values of quantities

The International System of Units 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. In most languages multiple whitespace characters are treated the same as a single whitespace character ; 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.
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.
Most languages only recognize ASCII characters as whitespace, or in some cases Unicode newlines as well, but not most of the characters 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 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 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. 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 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". It was used in BCDIC, EBCDIC, and ASCII-1963.