Ruby accessibility gap in WCAG and upcoming proposal for WCAG 2.3

Dear I18N WG colleagues,

In yesterday’s AG WG call, I realized something that I had not fully
appreciated before: PDF documents are fully within scope for WCAG.  Given
that, I want to raise an issue that is both technical and architectural,
and is highly relevant to our group’s charter.

As you know, Japanese, Chinese, and some other writing systems require ruby
annotations to convey reading information that is essential for
comprehension.
However, WCAG currently includes no success criterion that ensures that the
relationship between base text and ruby annotations is preserved.

In HTML, this relationship is generally preserved through the ruby markup
model.  But in PDF, ruby is often represented as a separate line of text,
resulting in a complete loss of semantic association, making the document
effectively unreadable for users relying on assistive technologies.

Meanwhile, ISO 32000-2 (PDF 2.0) defines a correct ruby annotation
structure, and PDF/UA includes guidance aligned with it.  I l learned from
somebody in Adobe that their implementations fully support such
correct structures.  So the missing piece is not technical capability, but
rather the absence of a requirement in WCAG that would ensure this
association must be preserved.

I intend to propose a new success criterion in WCAG 2.3 requiring that
content preserve the explicit parent–ruby relationship in a way that allows
user agents and assistive technologies to:

   - hide or show ruby,
   - adjust visual presentation (size, spacing, color), and
   - convey the association programmatically for TTS.

Before drafting concrete wording, I plan to explain the rationale and show
a short example in our call this Friday.
After that, I will prepare a proposal text, and I would appreciate the
Working Group’s feedback before submitting it to AG WG.

I believe this can be a constructive and important contribution from I18N
WG to WCAG 2.3, addressing a longstanding architectural gap.

Best regards,
Makoto