ISO/IEC 646 ISO/IEC 646 is a set of International Organization for Standardization, ISO/International Electrotechnical Commission, IEC standards, described as ''Information technology — ISO 7-bit coded character set for information interchange' ...

(commonly known as

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...

) and related standards including

ISO 8859 ISO/IEC 8859 is a joint ISO and IEC series of standards for 8-bit character encodings. The series of standards consists of numbered parts, such as ISO/IEC 8859-1, ISO/IEC 8859-2, etc. There are 15 parts, excluding the abandoned ISO/IEC 8859-12. ...

and

Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, wh ...

, a graphic character is any character intended to be written, printed, or otherwise displayed in a form that can be read by humans. In other words, it is any encoded character that is associated with one or more glyphs.

ISO/IEC 646

In ISO 646, graphic characters are contained in rows 2 through 7 of the code table. However, two of the characters in these rows, namely the

space 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 ...

SP at row 2 column 0 and the

delete character The delete control character (also called DEL or rubout) is the last character in the ASCII repertoire, with the code 127. It is supposed to do nothing and was designed to erase incorrect characters on paper tape. It is denoted as in caret notat ...

DEL (also called the rubout character) at row 7 column 15, require special mention. The space is considered to be ''both'' a graphic character and a control character in ISO 646. It can have a visible form, and also a control function (moving the print head). The delete character is strictly a control character, not a graphic character. This is true not only in ISO 646, but also in all related standards including Unicode. However, many modern character sets deviate from ISO 646, and as a result a graphic character might occupy the position originally reserved for the delete character.

Unicode

In Unicode, Graphic characters are those with General Category Letter, Mark, Number, Punctuation, Symbol or Zs=space. Other code points (General categories Control, Zl=line separator, Zp=paragraph separator) are Format, Control, Private Use, Surrogate, Noncharacter or Reserved (unassigned).https://www.unicode.org/versions/Unicode5.2.0/ch02.pdf#G25564 Chapter 2, table 2.3

Spacing and non-spacing characters

Most graphic characters are spacing characters, which means that each instance of a spacing character has to occupy some

area Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape or planar lamina, while '' surface area'' refers to the area of an ope ...

in a graphic representation. For a

teletype A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. Init ...

or a

typewriter A typewriter is a mechanical or electromechanical machine for typing characters. Typically, a typewriter has an array of keys, and each one causes a different single character to be produced on paper by striking an inked ribbon selectivel ...

this implies moving of the carriage after typing of a character. In the context of

text mode Text mode is a computer display mode in which content is internally represented on a computer screen in terms of characters rather than individual pixels. Typically, the screen consists of a uniform rectangular grid of ''character cells'', each ...

display, each spacing character occupies one rectangular character box of equal sizes. Or maybe two adjacent ones, for non-alphabetic characters of East Asian languages. If a text is rendered using

proportional font A typeface (or font family) is the design of lettering that can include variations in size, weight (e.g. bold), slope (e.g. italic), width (e.g. condensed), and so on. Each of these variations of the typeface is a font. There are thousands ...

s, widths of character boxes are not equal, but are

positive Positive is a property of positivity and may refer to: Mathematics and science * Positive formula, a logical formula not containing negation * Positive number, a number that is greater than 0 * Plus sign, the sign "+" used to indicate a posi ...

. There exist also ''non-spacing'' graphic characters. Most of

non-spacing character In digital typography, combining characters are characters that are intended to modify other characters. The most common combining characters in the Latin script are the combining diacritical marks (including combining accents). Unicode also ...

s are ''

modifiers In linguistics, a modifier is an optional element in phrase structure or clause structure which ''modifies'' the meaning of another element in the structure. For instance, the adjective "red" acts as a modifier in the noun phrase "red ball", provi ...

'', also called combining characters in Unicode, such as

diacritic A diacritic (also diacritical mark, diacritical point, diacritical sign, or accent) is a glyph added to a letter or to a basic glyph. The term derives from the Ancient Greek (, "distinguishing"), from (, "to distinguish"). The word ''diacriti ...

al marks. Although non-spacing graphic characters are uncommon in traditional code pages, there are many such in Unicode. A combining character has its distinct glyph, but it applies to a character box of another character, a spacing one. In some historical systems such as

line printer A line printer prints one entire line of text before advancing to another line. Most early line printers were impact printers. Line printers are mostly associated with unit record equipment and the early days of digital computing, but the ...

s this was implemented as

overstrike In typography, overstrike is a method of printing characters that are missing from the printer's character set. The character is created by placing one character on another one — for example, overstriking "L" with "-" results in printing a " ...

. Note that not all modifiers are non-spacing – there exists

Spacing Modifier Letters Spacing Modifier Letters is a Unicode block containing characters for the IPA IPA commonly refers to: * India pale ale, a style of beer * International Phonetic Alphabet, a system of phonetic notation * Isopropyl alcohol, a chemical compound ...

Unicode block.

References

{{Reflist Character encoding

ISO/IEC 646

Unicode

Spacing and non-spacing characters

See also

References