Shift Out and Shift In characters
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. This was used, for instance, in the Russian character set known as KOI7, where SO starts printing Russian letters, and SI starts printing Latin letters again. SO/SI control characters also are used to display VT-100 pseudographics, and emoji (Japanese picture icons) on SoftBank Mobile. ISO/IEC 2022 standard specifies their generalized usage.
Some older printers used these characters to control special features, such as changing the font or ink color. On the Teletype Model 38, SO switched to red printing while SI switched back to black printing.
- "The Linux Programmer's Manual". Retrieved 2012-11-16.
See also 
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