Mention that ruby is not just for schoolkids and other esoteric users

[r12a]

1. Introduction
   https://www.w3.org/TR/html-ruby-extensions/#intro

Typically ruby is used in East Asian scripts to provide phonetic transcriptions of obscure and little known characters, characters that the reader is not expected to be familiar with (such as children or foreigners learning to write), or characters that have multiple readings which can’t be determined by the context (eg. some Japanese names). For example it is widely used in educational materials and children’s texts. It is also occasionally used to convey information about the meaning of ideographic characters.

This somewhat intimates that 'ordinary' people don't usually need ruby and its use is rather restricted to special cases, but actually it is normal to find ruby in any novel, comic, or in-flight magazine that a person picks up. Perhaps change the penultimate sentence to

For example it is widely used in educational materials and children’s texts, but it can also be readily found in many types of literature and signage.