Monospace or non-proportional fonts, unlike proportional fonts, have a fixed character width. The "i" therefore takes up the same space as an "o". However, due to the different actual space requirements of the characters, there are often larger gaps in the typeface. For example, in monospace fonts, the optical gap between o and i (oi) is larger than between o and a (oa). Since their appearance is clearly different from proportional fonts, monospace fonts, for example, are often used in text documents to mark up source code examples.