空白文字

Unicodeには、視覚的に記号を表示する必要がある場面で、さまざまな空白文字を表すために使用できる可視文字もいくつか用意されています。

Exact space

• The Cambridge Z88 provided a special "exact space" (code point 160 aka 0xA0) (invokable by key shortcut ⌑+SPACE^[19]), displayed as "…" by the operating system's display driver.^[20][21] It was therefore also known as "dot space" in conjunction with BBC BASIC.^[20][21]
• 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).^[20][21]

• The Braille Patterns Unicode block contains U+2800⠀BRAILLE PATTERN BLANK, 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.^[22]
• 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 (U+3164ㅤHANGUL FILLER). 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.^[23]
  • 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 (U+115FᅟHANGUL CHOSEONG FILLER, U+1160ᅠHANGUL JUNGSEONG FILLER).^[24]
  • Additionally, a Halfwidth Hangul Filler is included in the Halfwidth and Fullwidth Forms (U+FFA0ﾠHALFWIDTH HANGUL FILLER), which is used when mapping from encodings which include characters from both Johab (or Wansung) and N-byte Hangul (or its EBCDIC counterpart), such as IBM-933, which includes both Johab and EBCDIC fillers.^[25][26]

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.^[27]

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

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 above for a complete list.

Em dashes used as parenthetical dividers, and en dashes when used as word joiners, are usually set continuous with the text.^[28] 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  . 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.

In most programming languagesyntax, 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".^[29] The HTTP network protocol requires different types of whitespace to be used in different parts of the protocol; it requires single space characters between items in the status line, a CR/LF pair at the end of a line, and "linear whitespace" in header values.^[30]

Typical command-line parsers use the space character to delimitarguments. 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.

If, for example, a user wanted to view the contents of a directory named foo bar by using the ls (list) command, and they did so by entering the command as:

lsfoobar 

the command would, instead, attempt to list files or directories named foo and bar. The correct syntax would specify only a single argument by enclosing it in double quotes:

ls"foo bar"

Or, alternatively, they could choose to leave out the double quotes and instead escape the space with a backslash:

lsfoo\ bar 

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 for identification purposes, in a manner similar to but less overtly obvious than the way comments in code can. This can be of benefit in proving an infringement of license or copyright claim if the code was blatantly copied and pasted.

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 is U+2422␢BLANK SYMBOL, which was used on coding forms in the early years of computer programming. Keypunch operators interpreted it as an "explicit space".^[16] It was used in BCDIC,^[16]EBCDIC,^[16] and ASCII-1963.^[16]