Bopomofo light tone mark on the Web

[Richard Ishida]

At the W3C we are trying to understand how to handle the bopomofo in 
phonetic annotations (for the CSS Ruby spec).

Please see a write up of the background and some relevant questions at 
http://rishida.net/scripts/bopomofo/ontheweb

A key question relates to the light tone.

The light tone falls out from most IMEs and is displayed, for example, 
by Keynote's phonetic guide function, after the bopomofo letters. In 
pretty much all the vertical bopomofo we have seen, and in pretty much 
all dictionaries we have seen (horizontal or vertically set) the light 
tone, however, is displayed before the bopomofo letters.

Note that modern dictionaries appear to be actually moving the character 
code into first position in the syllable to achieve this.

We'd like to know:

1. is anyone aware of any ruling about where the light tone should 
appear and/or be stored in the text stream?

2. does it (really) matter if text sometimes contains the light tone 
character  before the syllable and sometimes trailing, depending on 
where people prefer to put it?

(Obviously, there's a theoretical issue for sorting and searching if it 
is sometimes in one place and sometimes in another, but it may be that 
both places are actually viable positions.)

3. is there any font/rendering software out there that makes the light 
tone appear at the start of a syllable, when the character is actually 
at the end of the syllable?

cheers,

ri