the graphical codes, excluding the space) to invoke characters from an alternative set, and the Shift In () control would change them back. In an 8-bit environment, instead of using shift codes, the eighth bit was set on a byte referencing the additional graphic character set. This meant that bytes 0xA1 through 0xFE were used for the additional graphic characters. The C0 control characters, being unaffected by the shift state of a 7-bit code, were to always be represented in an 8-bit code with the eighth bit unset. The consequently otherwise-unused bytes in the range 0x80 through 0x9F could be used for additional control codes, which would instead be represented as 0x1B 0x40 through 0x1B 0x5F (ESC @ through ESC _) in a 7-bit code. These additional control codes become known as the C1 control codes. To retain compatibility with the 7-bit representation, the behaviour of bytes 0xA0 and 0xFF was originally left undefined. The first C1 control code set to be registered for use with ISO 2022 was DIN 31626, a specialised set for bibliographic use which was registered in 1979. The general-use ISO/IEC 6429 set was registered in 1983, although the ECMA-48 specification upon which it was based had been first published in 1976. Further editions of the standards altered the provisions to an extent. For instance, a further revision to ECMA-35 and ISO 2022 in 1985 introduced the concept of a 96-code graphical character set. In an 8-bit code, this allowed the entire range from 0xA0 to 0xFF to be used for graphical characters. Use of 96-code sets also meant that the meaning of the bytes 0x20 and 0x7F in the corresponding 7-bit code could differ from "Space" and "Delete", unless the code was in the Shift In state. Using 96-code sets for the G0 (Shift In) set was not made possible. In accordance with this revised 8-bit ISO 2022 code structure, ISO 8859 defines sets of characters to be encoded over 0xA0–FF, in combination with the ASCII graphical characters over 0x20–7E, and reserves the bytes outside of these ranges for use as non-graphical codes by other specifications such as ISO/IEC 6429. Unicode inherits its first 256 code points from ISO 8859-1, hence also incorporating a range reserved for a C1 control code set, although it mostly leaves their function to be defined by higher level protocols, with ISO/IEC 6429 suggested as a default. C1 control codes