The Internationalization Working Group has published a First Public Working Draft of Rules for Simple Placement of Japanese Ruby. This document provides a simple set of rules for placement of Ruby text in Japanese typography that can be used as a minimum baseline for implementers and specification writers.

Ruby is the name given to the small annotations in Japanese content that are rendered alongside base text, usually to provide a pronunciation guide, but sometimes to provide other information.

Original source: https://www.w3.org/blog/news/archives/8593