eproduces è on the Macintosh U.S. keyboard layout. On a typewriter, this was accomplished mechanically by striking the diacritic mark without advancing the carriage (thus, the paper is still in the position to accept the next letter at the same spot the diacritic was placed). On a computer, the key instead temporarily changes the mapping of the keyboard for the next keypress.
For example, if a keyboard has a dead key
`, the French character e accent grave (è) can be generated by pressing first
e. Usually pressing a dead key followed by space produces the character denoted by the dead key; e.g.
space results in “¨”.
By construction, this has no restrictions on a typewriter, so you could place one on a q for example: With Unicode combining characters, this might look like q́. On the other hand, computers often do not work this way;
q results in ´q.
In Microsoft Word, using the Control key with a key that usually resembles the diacritic (e.g.
^ for a circumflex) acts as a dead key. Many non-English keyboard layouts have dead keys directly on the keyboard. The US-International keyboard layout available on Windows and the X Window System place dead keys directly on similar-looking punctuation marks.
Old computer systems such as the MSX often had a special labeled “dead key”, which in combination with the Ctrl and Shift keys could add the accents ´, `, ˆ and ¨ to vowels that were typed subsequently.