[1] ISO/IEC TR 10176:1998, "Information technology -- Guidelines for the preparation of programming language standards", ISO/IEC, 1998-09-01 (Second edition).

[2] JIS TR X 0031:2000, "Information technology -- Guidelines for the preparation of programming language standards", JISC http://www.jisc.go.jp/, 2000-06-01, will be expired on 2005-07-31. (TR type III) (IDT with ISO/IEC TR 10176:1998.)

[3] ISO/IEC TR 10176:1998 Annex A

The repertoire recommended consists of characters that are used to write different natural langauges of the world, and consists of letters, ideographic and syllabic characters, digits, and some marks.
Attention is drawn to that using extended repertoire for identifiers may impact source code portability.