In typewriters, a typist would, for example, type a lowercase letter "a" with acute accent (á) by typing a lowercase letter "a" then backspace, and then the acute accent key (also known as overstrike). This 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 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 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 placing the base letter at that position.