 Morse code

Morse code encodes characters using short and long signals, conventionally dots and dashes, together with timed gaps. In International Morse code, a dash lasts three dot units; gaps within a character last one unit, between characters three, and between words seven. Thus character boundaries are part of the encoding.

For example, $S$ is three dots and $O$ is three dashes. If gaps are erased, the dot-dash strings alone are not a prefix code: the code for $E$, one dot, is a prefix of that for $I$, two dots. This makes Morse code a useful example of how a communication code can rely on timing as well as symbol choices.^[ref]