Backspace

File:Blickensderfer model 7, 1909.jpg|thumb|An early typewriter with a backspacer[sic] key. (Blickensderfer Model 7) Although the term "backspace" is the traditional name of the key which steps the carriage back and/or deletes the previous character, the actual key may be labeled in a variety of waysfor example delete, erase, or with a left pointing arrow. Full-size Mac keyboards have two keys labeled delete; a key that functions as a backspace key, and a key that functions as a delete key. Smaller Mac keyboards, such as laptop keyboards, have only a key that functions as a backspace key. Full-size PC keyboards have a backspace key (in the main section) and two delete keys (in the extended area). ==Combining characters==

With some typewriters, a typist would, for example, type a lowercase letter A with acute accent (á) by typing a lowercase letter A, backspace, and then the acute accent key. This technique (also known as overstrike) is the basis for such spacing modifiers in computer character sets such as the ASCII caret (^, for the circumflex accent). Backspace composition no longer works with typical modern digital displays or typesetting systems. It has to some degree been replaced with the combining diacritical marks mechanism of Unicode, though such characters do not work well with many computer fonts, and precomposed characters continue to be used. (Some software like TeX or Microsoft Windows use the opposite method to apply a diacritical mark, namely typing the accent first, and then the base letter to be accented.) ==Use in computing==

Common use In modern systems, the backspace key is often mapped to the delete character (12710, 7f16, in ASCII), although the backspace key's function of deleting the character before the cursor remains. In computers, backspace can also delete a preceding newline character, something generally inapplicable to typewriters. ^H Pressing the backspace key on a computer terminal would generate code 0810, the ASCII control code (Backspace), which would delete the preceding character. That control code could also be accessed by pressing +, as H is the eighth letter of the Latin alphabet. Terminals which did not have the backspace code mapped to the function of moving the cursor backwards and deleting the preceding character would display the symbols ^H (caret, H) when the backspace key was pressed. Even if a terminal did interpret backspace by deleting the preceding character, the system receiving the text might not. Then, the sender's screen would show a message without the supposedly deleted text, while that text, and the deletion codes, would be visible to the recipient. This sequence is still used humorously for epanorthosis by computer literates, denoting the deletion of a pretended blunder, much like a strikethrough; in this case, however, the ^H symbol is faked by typing a regular '^' followed by typing a regular 'H'. For example: :Be nice to this fool^H^H^H^H''gentleman; he's visiting from corporate HQ.'' Related sequences In some contexts, ^W is used as a shortcut to delete the previous word, such as in the Berkeley Unix terminal line discipline. This shortcut has also made it into the insert mode of the Vi text editor and its clone Vim. Similarly, ^U deletes a line. ==Notes==