Bopomofo light tone mark on the Web

From: Richard Ishida <>
Date: Wed, 04 Feb 2015 12:40:01 +0000

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

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?


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