Shift In

Shift Out (SO) and Shift In (SI) are ASCII control characters 14 and 15, respectively (0x0E and 0x0F.) The original meaning of those characters provided a way to shift, hence the nomenclature, a coloured ribbon, split longitudinally usually with red and black, up and down to the other colour in an electro-mechanical typewriter or teleprinter to automate the same function of manual typewriters. Black was the conventional ambient default colour and so was shifted "in" or "out" with the other colour on the ribbon. Later advancements in technology, such as the IBM Selectric typewriter, instigated use of this function for switching to a different font or character set and back.
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