@vindex tab-width
Indentation is often performed with the help of @dfn{tab characters}
-(ASCII code 9), which are displayed as a stretch of empty space
+(@acronym{ASCII} code 9), which are displayed as a stretch of empty space
extending to the next @dfn{display tab stop}. By default, there is
one display tab stop every eight columns; the number of columns is
determined by the variable @code{tab-width}. You can insert a single