From: John H. Jenkins (firstname.lastname@example.org)
Date: Wed Jun 09 2010 - 12:55:40 CDT
Both a decimal 2 and a hexadecimal 2 are an ideogram representing the abstract concept of "two-ness," and the latter is derived typographically from the former (and, indeed, currently looks exactly like it). This is comparable to a Chinese 二 and a Japanese 二, which we've unified.
Unicode encodes characters, not glyphs. In order to separately encode a hexadecimal-2 separately from an decimal-2, you'd either have to show either that the two are, in fact, inherently different characters (in which case you'd better be prepared to separately encode the octal-2 and the duodecimal-2 et al.), or you'd have to two that widespread existing practice treats them as distinct or at least draws them distinctly.
(And before anybody raises the objection, nobody treats the Chinese 二 and Japanese 二 as distinct. There are other sinograms which look different when designed for Chinese use and Japanese use and some people would like to treat them as distinct for that reason, but historically and in current practice, this is not actually done.)
Indeed, current practice universally treats decimal-0 through decimal-9 as hexadecimal-0 through hexadecimal-9 and letter-A/a through letter-F/f as hexadecimal-10 through hexadecimal-15. That practice would have to change before any serious attempt at encoding "hexadecimal digits" would be considered. And using letters for numerals has a long and distinguished history despite the inherent ambiguities, so there is ample precedent for the current practice.
Yes, this does create a chicken-and-egg problem, and whether or not this will have a long-term impact on the creation or adoption of new alphabets or new typographic practice is an interesting one. That, however, is irrelevant to how Unicode does things.
In re the tonal system specifically, I note that it uses a glyph for hexadecimal-10 which looks (to me, at least) identical with a glyph for decimal-9. This IMHO represents a serious impediment to the system ever being adopted. I will, however, gladly be proven wrong.
John H. Jenkins
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