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The interpretation of the control key with non-ASCII ("foreign") keys also varies between systems. Control characters are often rendered into a printable form known as caret notation by printing a caret (^) and then the ASCII character that has a value of the control character plus 64. Control characters generated using letter keys are thus ...
In 1973, ECMA-35 and ISO 2022 [18] attempted to define a method so an 8-bit "extended ASCII" code could be converted to a corresponding 7-bit code, and vice versa. [19] In a 7-bit environment, the Shift Out would change the meaning of the 96 bytes 0x20 through 0x7F [a] [21] (i.e. all but the C0 control codes), to be the characters that an 8-bit environment would print if it used the same code ...
In a broader sense, other non-printing format characters, such as those used in bidirectional text, are also referred to as control characters by software; [2] these are mostly assigned to the general category Cf (format), used for format effectors introduced and defined by Unicode itself.
[12]: 13.1 The escape sequences consist only of bytes in the range 0x20—0x7F (all the non-control ASCII characters), and can be parsed without looking ahead. The behavior when a control character, a byte with the high bit set, or a byte that is not part of any valid sequence, is encountered before the end is undefined.
The implicit directional marks are non-printing characters used in the computerized typesetting of bi-directional text containing mixed left-to-right scripts (such as Latin and Cyrillic) and right-to-left scripts (such as Persian, Arabic, Syriac and Hebrew).
ASCII was incorporated into the Unicode (1991) character set as the first 128 symbols, so the 7-bit ASCII characters have the same numeric codes in both sets. This allows UTF-8 to be backward compatible with 7-bit ASCII, as a UTF-8 file containing only ASCII characters is identical to an ASCII file containing the same sequence of characters.
On many Unix systems and early dial-up bulletin board systems the only common standard for box-drawing characters was the VT100 alternate character set (see also: DEC Special Graphics). The escape sequence Esc ( 0 switched the codes for lower-case ASCII letters to draw this set, and the sequence Esc ( B switched back:
If we define control characters as non-graphic, or as having a special meaning for an output device (e.g. printer or text terminal) then any escape character for this device is a control one. But escape characters used in programming (such as the backslash , "\") are graphic, hence are not control characters.