Width — Assume a column width of 2 for each supplementary character. This works for the HKSCS code page, but not for other supplementary characters
Word breaking — Follow the heuristic rules already in place for UTF-8. Supplementary characters are considered as separate words, like 3-byte UTF-8 characters
Case rules — No case transformations are applied to supplementary characters. This works for HKSCS, but not for other supplementary characters (in Unicode 3.1, Deseret characters are the only supplementary characters with case mappings)