Editing Backspace (section)

==Combining characters==
In some<ref group="note">Many typewriters don't advance accent characters, thus no backspace is needed where the accent is typed ahead of the letter it is to be combined with. However, even with such machines, the backspace is still used to produce certain other characters, e.g. for combining "o" with "/" to make "ø".</ref> 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.<ref group="note">There is no reason why a digital display or typesetting system could not be designed to allow backspace composition, a.k.a. overstrike, if an engineer chose to do that. As most contemporary computer display and typesetting systems are raster graphics-based rather than character-based (as of 2012), they make overstrike actually quite easy to implement. However, the use of proportional-width rather than fixed-width (monospaced) fonts makes the practical implementation of overstrike more complicated, and the original physical motivation for the technique is not present in digital computer systems.</ref> It has to some degree been replaced with the [[combining diacritical mark]]s mechanism of [[Unicode]], though such characters do not work well with many fonts, and precomposed characters continue to be used. Some software like [[TeX]] or [[Microsoft Windows]] use the opposite method for diacritical marks, namely positioning the accent first, and then the base letter on its position.