C1 CONTROLS in THE CODE CHARTS
V.S. Umamaheswaran, IBM
The subject of dealing with C1 controls in Unicode has been brought up for discussion in the past, in the Tredyffrin meeting as well as in the Redmond meeting. This document consolidates the proposal from these meetings.
Unicode standard Chapter 12.1, Section on C1 control codes has the last sentence – "However, in the absence of specific application uses, they may be interpreted according to the semantics specified in IS 6429.".
ISO/IEC 10646 also suggests the default value to be used for C1 area is to be taken from IS 6429.
There is a similar statement for the C0 control set also, though some of the control characters of C0 are explicitly used in Unicode.
When one looks at the code charts in conjunction with the above, columns 000 and 001 showing C0 controls have dotted squares with C0 mnemonics from IS 6429, and a listing of these control character names in the name table.
However, the C1 space columns 008 and 009 are simply shown with a dotted square and words CTRL shown in them. The corresponding U+0080 through U+009F are also not shown in the name table.
This proposal is to add the mnemonics of IS 6429 C1 similar to C0 set, in the chart and add the list of control character names similar to C0 set. A list of the control character names and their corresponding mnemonics of ISO 6429 C1 controls can be found in the contribution on UTF-EBCDIC (L2/98-257).
The main reasons are for clarity in referring to these characters, consistency in presentation of the information. The second reason is to prevent misuse of this area for purposes other than a control or for uses similar to the Private Use Area. The intent of safe passage for C0 captured under the paragraph on C0 control codes is equally applicable to the C1 space.
Further we should request SC2 WG2 to also fix the corresponding code charts in 10646 regarding the C1 area.