Text-to-Speech Rendering of Electronic Documents Containing Ruby: User Requirements

The primary purpose of ruby annotations is to indicate how to pronounce CJK ideographic characters, a practice known as Furigana (see also JLReq terminology ).

In contemporary usage, it is uncommon to attach ruby annotations to all CJK ideographic characters in a given document. Instead, it is more common to attach ruby annotations to only some of the CJK ideographic characters.

Ruby annotations find their application in various contexts, including trade books, newspapers, textbooks, teaching materials, and more, but are rarely utilized in business documents.

Even for simple CJK ideographic characters, ruby annotations may be added for some users who have particular difficulties with CJK ideographic characters (in electronic documents, it is easy to make ruby annotations visible or invisible based on user preferences). Such ruby annotations are referred to as "furigana added for enhanced accessibility".

Some simple CJK ideographic characters have more than one possible reading and thus require ruby annotations for disambiguation. This is common for names of people and places. For example, 山崎 (a person's name) may be read as YAMAZAKI or YAMASAKI.

When ruby annotations are applied only to selected CJK ideographic characters in a document, typically only the first occurrence of such characters or words receives an annotation, and subsequent occurrences do not. This practice assumes that users will learn the correct pronunciation from the first occurrence.

Especially in Japan, ruby annotations are also used to indicate something different from the reading of a CJK ideographic character. Such ruby annotations are referred to as Gikun . Gikun is commonly employed in light novels and comics.

Here are some examples of Gikun:

• 敵 とも (where 敵 means 'enemy' and とも means 'friend'). The combination means 'frenemy'.
• 生命 いのち (where the typical reading of 生命 is SEIMEI rather than いのち (INOCHI), both of which mean 'Life')
• 背景 バック (where the typical reading of 背景 is HAIKEI rather than バック (back), an English translation)
• 牛乳 ミルク (where the typical reading of 牛乳 is GYUUNYUU rather than ミルク (milk), an English translation)

Even when Gikun is used for a compound word, it is unlikely to be repeated for later occurrences of the same word. Moreover, different GIKUN may be added for subsequent occurrences of the same word. For example, the next occurrence of 生命 may well be 生命 ライフ where ライフ (life) is an English translation.

Unusual names of people in Japan are typically written using CJK ideographic characters but are pronounced quite differently from the standard reading of these characters. For instance, 男 あだむ is an unusual name, where 男 (usually read as OTOKO) means 'man', and あだむ represents 'Adam' in Kana.

Character names in comics, animations, and light novels can sometimes be extremely challenging to pronounce. Many of the character names in Demon Slayer (Kimetsu no Yaiba) fall into this category. For example, almost no one can read 不死川 玄弥 as SHINAZUGAWA GENNYA without assistance.

Names of places can also be difficult to read due to historical reasons. For instance, 神居古潭 かむいこたん , 温根沼 おんねとう , 音威子府 おといねっぷ are names of places in Hokkaido (the northern island of Japan). These names are challenging to pronounce because they originated from the Ainu language , which is entirely different from the Japanese language.

In many instances, the first occurrence of an unusual name is accompanied by a ruby annotation, but subsequent occurrences are not.

Interlinear notes resemble ruby annotations in appearance. A note in JLreq introduces interlinear notes as follows:

In the example shown in a figure referenced in the quoted note ("An example of a note in inter lines") , 徳川慶喜 (Tokugawa Yoshinobu) is accompanied by an interlinear note "1837-1913 江戸幕府最後の将軍 " (1837-1913 the last shogun of the Edo shogunate). Other examples are: a modern kana phrase as an interlinear note for a historical kana phrase, a standard Japanese expression as an interlinear note for an expression in a dialect, a modern CJK ideographic character as an interlinear note for a traditional CJK ideographic character, an English text chunk as an interlinear note for a Japanese text chunk, and an official name as an interlinear note for an abbreviated name.

One could argue that HTML ruby elements should not be used for representing interlinear notes (see Kobayashi Sensei's mail in Japanese ). However, it is not difficult to imagine that ruby elements are actually used for representing interlinear notes.

Ruby annotations can be used for purposes other than indicating the reading of CJK ideographic text. For example, they may be applied to foreign-language text written in non-native scripts, chemical formulas, mathematical expressions, or other specialized notations, in order to convey pronunciation or supplementary information.

However, such uses of ruby annotations fall outside the scope of this note. This document focuses exclusively on ruby annotations associated with CJK ideographic text, where language-dependent reading behavior and accessibility considerations raise specific and non-trivial issues.

A sequence of characters can be accompanied by two ruby annotations, typically consisting of Furigana and either GIKUN or an interlinear note . In an example provided in JLreq ("An example of ruby annotations attached to both sides of the base characters"), 東南 is accompanied by たつみ and とうなん . Here 東南 means 'southeast', with とうなん (TOUNAN) serving as Furigana , and たつみ (TATSUMI) as GIKUN , as 辰巳 (read as TATSUMI ) indicates the same direction as 東南 .

We offer two additional illustrative examples.

In this example, とうよう serves as Furigana , while オリエント is used as Gikun

In this example, おだのぶなが serves as Furigana , while "1534〜82" is presented as an interlinear note .

The strategies discussed in this section for reading aloud content that contains ruby annotations are inherently language-dependent. The presence of ruby annotations does not necessarily imply that the annotations themselves should be read aloud. The appropriateness, effectiveness, and potential drawbacks of a given strategy depend on the writing system, linguistic conventions, and typical roles that ruby annotations play in each language.

This Note focuses primarily on Japanese and Chinese, which both employ ruby annotations but do so in fundamentally different ways. In Japanese, ruby annotations can be essential for correct interpretation and comprehension of the base text in read-aloud scenarios. As a result, how ruby annotations are handled during read-aloud processing can have a significant impact on user experience, and careful selection among alternative strategies is required.

In contrast, in Chinese, ruby annotations such as pinyin or zhuyin are typically used as auxiliary pronunciation aids and are not generally required for intelligible read-aloud output. In many practical reading scenarios, text-to-speech (TTS) or other read-aloud output based solely on the ruby base text is sufficient. Reading ruby annotations aloud may in some cases introduce confusion, particularly when the assumptions underlying the annotations do not align with those of the read-aloud output.

The analysis of Chinese reading practices in this Note is limited. While some general observations are provided to inform the discussion of read-aloud strategies, a comprehensive treatment of Chinese reading practices — including dialectal variation, prosodic information, and phonological detail — is beyond the scope of this version of the Note.

The strategies described in the following subsections should therefore not be interpreted as universally applicable recommendations. User agents and assistive technologies are expected to take the target language, content type, and usage context into account when selecting or implementing a strategy for reading aloud content that includes ruby annotations.

In this option, This strategy reads aloud both ruby bases and ruby annotations are read aloud (double reading). Many implementations (screen readers, in particular) support only the option of reading both ruby bases and annotations. this strategy. For example, foo bar is read aloud as 'foo bar' or 'bar foo'.

In this option, This strategy reads aloud ruby annotations are read aloud but without reading the ruby bases are not. bases. For example, foo bar is read aloud as 'bar'.

In this option, This strategy reads aloud ruby bases are read aloud but without reading ruby annotations are not. annotations. For example, foo bar is read aloud as foo.

Small kana characters ゃ , ゅ , ょ , and っ are too small when they appear in ruby annotations. For this reason, instead of these small characters, full-size kana characters や , ゆ , よ , and つ are used in ruby annotations.

However, since full-size kana characters are pronounced differently from small kana, ruby annotations containing full-size kana are read aloud differently.

CSS has a mechanism for overcoming this problem. Value ' full-size-kana ' of the text-transform property as specified in CSS Text converts small kana characters to full-size kana. It is thus possible to use small kana in ruby annotations while rendering them using full-size kana. Text-to-speech engines can provide correct results even when ruby annotations are read aloud.

When attaching a ruby annotation to a compound word consisting of multiple CJK ideographic characters in an HTML or EPUB document, one way is to create a single HTML ruby element for the entire word. However, in some cases, a separate ruby element is created for each CJK ideographic character. For example, to attach the ruby annotation せいめい to the word 生命 (meaning “life” in Japanese), the typical approach is to create a single ruby element for this word. This ruby element may have a single rt element for “せいめい” or two rt elements (one for “せい” and another for “めい”). However, it is not entirely uncommon to see two ruby elements for this word: one for “生” and another for “命”.

Some people argue that creating a ruby element per compound word is better than creating a ruby element for each character in a compound word. They argue that it becomes easier for the text-to-speech engine to maintain a correspondence table between ruby bases and ruby annotations so that subsequent occurrences of the compound word without ruby can be pronounced correctly.

Meanwhile, others argue that there is a good reason to attach ruby annotations to some, but not all, characters in a compound word. For example, consider 佳人 , where 佳 is taught in junior high schools while 人 is taught in the first grade of elementary schools. Therefore, it makse sense to attach a ruby annotation to 佳 only (one ruby element for 佳 and no ruby element for 人 ). Similarly, it is reasonable to attach ruby annotations to the first and third CJK idegraphic characters in 屯田兵 only but not to the second one (thus, two ruby elements).

Although furigana added for enhanced accessibility is necessary for those readers who have particular difficulties with CJK ideographic characters, it is unnecessary or slightly disturbing for others. If furigana added for enhanced accessibility is distinguishable from normal furigana, it can be made visible or invisible depending on user preferences. It is thus desirable to have a standardized way to indicate furigana added for enhanced accessibility.

In 3. Which should be read aloud, ruby bases or ruby annotations, or both? , we have seen that ruby annotations used as gikun or interlinear notes should be read aloud differently from the other cases. Therefore, it is important to be able to distinguish ruby annotations used as gikun or interlinear notes from other ruby annotations in order to support appropriate reading behavior. How such distinctions are made — whether through linguistic analysis, lexical resources, markup conventions, or other means — is outside the scope of this document.

[ SSML ] employs symbol collections (such as IPA and [ JEITA_IT-4006 ]) to represent the sounds of human languages. Phonemic and phonetic pronunciations are conveyed through sequences of these symbols.

[ epub-32 ] allows the use of SSML attributes within XHTML content documents in EPUB publications. In [ epub-33 ], these attributes are relocated to [ epub-tts-10 ]. Meanwhile, the W3C Accessible Platform Architectures Working Group is developing [ spoken-html ], which outlines two potential methods for incorporating SSML attributes into HTML elements.

In Japan, SSML finds extensive application in digital textbooks, adopted by the biggest textbook publisher in Japan. However, it has been noted that attaching SSML attributes to CJK ideographic characters significantly raises authoring costs. In the case of DAISY textbooks in Japan, SSML is not used, as they contain recorded voice. Trade books in Japan do not typically employ SSML either.

PLS ([ PRONUNCIATION-LEXICON ]) enables the use of pronunciation lexicons, which map words to sequences of symbol collections such as those found in IPA or [ JEITA_IT-4006 ].

While SSML attributes are embedded within XHTML content documents in EPUB publications, PLS lexicons in EPUB publications are stored externally to and referenced by XHTML content documents (see Pronunciation Lexicons section in [ epub-tts-10 ]). As of the present, [ spoken-html ] does not offer a mechanism for associationg PLS lexicons with HTML documents.

PLS is a robust tool for rendering unusual names of people and places in text-to-speech applications. In particular, PLS allows every occurrence of a word or phrase to be consistently pronounced, regardless of the presence of ruby annotations. At the time of this writing, PLS is used by at least one digital textbook publisher in Japan.