(GS), IS4 (FS). Locking shifts: LS0 (SI), LS1 (SO). Others: NUL, BEL, CAN, EM, SUB, ESC. ISO/IEC 2022 (ECMA-35) refers to the C0 locking shifts as LS0 and LS1 in 8-bit environments, and as SI and SO in 7-bit environments. The first, 1963 edition of ASCII classified as a device control, rather than a transmission control, and gave it the abbreviation DC0 ("device control reserved for data link escape"). Format (FE) codes define and actuate formatting (such as line breaks) which affects how graphical characters are laid out and rendered, as opposed to controlling other functions of hardware devices or having other side effects. The C0 format effectors are permitted in ISO/IEC 6429 , , and sequences. The information separators and C0 format effectors (minus ) are the only C0 control codes with semantics defined by the Unicode Standard, the interpretation of the remainder of the C0 controls being left to higher-level protocols. ISO/IEC 2022 (ECMA-35) requires that if C0 control code sets include the ten ASCII transmission control (TC) codes, they must be encoded at their ASCII locations. It also prohibits those ten transmission controls from being included in a C1 control code set, and prohibits transmission controls besides those ten from being included in a C0 control set. Modified C0 control code sets Although C0 control code sets usually preserve most of the ASCII control codes unchanged, a number are registered which replace certain control functions with alternatives. A selection of these, excluding those related to Videotex, are shown below. Other C0 control code sets Teletext defines an entirely different set of control codes. In formats where compatibility with ECMA-48's C0 control codes is not required, these control codes are sometimes mapped transparently to the Unicode C0 control code range (U+0000 through U+001F). C1 controls In parallel to the development of the 1972 edition of ISO 646, which revised the standard to introduce the concept of national versions of the code in addition to the US-originated ASCII, work was also underway with the purpose of defining extension mechanisms for ASCII, applicable to both 7-bit and 8-bit environments, which would be published as ECMA-35 and ISO 2022. These mechanisms were designed so that any conformant 8-bit code could be converted to a corresponding 7-bit code, and vice versa. In a 7-bit environment, the Shift Out () control would change the meaning of the 94 bytes 0x21 through 0x7E (i.e.