Pronunciation Use Cases

W3C Working Group Note

This version:
https://www.w3.org/TR/2020/NOTE-pronunciation-use-cases-20200317/
Latest published version:
https://www.w3.org/TR/pronunciation-use-cases/
Latest editor's draft:
https://w3c.github.io/pronunciation/use-cases/
Previous Versions:
https://www.w3.org/TR/2019/WD-pronunciation-use-cases-20190905/
Editors:
(Educational Testing Service)
(Deque System)
(Educational Testing Service)
(W3C)

Abstract

The objective of the Pronunciation Task Force is to develop normative specifications and best practices guidance collaborating with other W3C groups as appropriate, to provide for proper pronunciation in HTML content when using text to speech (TTS) synthesis. This document provides various use cases highlighting the need for standardization of pronunciation markup, to ensure that consistent and accurate representation of the content. The requirements from the user scenarios provide the basis for these technical requirements/specifications.

This specification is obsolete. Please see the latest Pronunciation Gap Analysis and Use Cases for the Pronunciation Use Cases.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

This document was published by the Accessible Platform Architectures Working Group as a Working Group Note.

Comments regarding this document are welcome. Please send them to public-pronunciation@w3.org (archives).

Publication as a Working Group Note does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the W3C Patent Policy.

This document is governed by the 1 March 2019 W3C Process Document.

1. Introduction

This section is non-normative.

This document provides use cases which describe specific implmentation approaches for introducing pronunciation and spoken presentation authoring markup into HTML5. These approaches are based on the two primary approaches that have evolved from the Pronunciation Task Force members. Other approaches may appear in subsequent working drafts.

Successful use cases will be those that provide ease of authoring and consumption by assistive technologies and user agents that utilize synthetic speech for spoken presentation of web content. The most challenging aspect of consumption may be alignment of the markup approach with the standard mechanisms by which assistive technologies, specifically screen readers, obtain content via platform accessibility APIs.

2. Use Case aria-ssml

2.1 Background and Current Practice

A new aria attribute could be used to include pronunciation content.

2.2 Goal

Embed SSML in an HTML document.

2.3 Target Audience

2.4 Implementation Options

aria-ssml as embedded JSON

When AT encounters an element with aria-ssml, the AT should enhance the UI by processing the pronunciation content and passing it to the Web Speech API or an external API (e.g., Google's Text to Speech API).

I say <span aria-ssml='{"phoneme":{"ph":"pɪˈkɑːn","alphabet":"ipa"}}'>pecan</span>.
You say <span aria-ssml='{"phoneme":{"ph":"ˈpi.kæn","alphabet":"ipa"}}'>pecan</span>.

Client will convert JSON to SSML and pass the XML string a speech API.

var msg = new SpeechSynthesisUtterance();
msg.text = convertJSONtoSSML(element.getAttribute('aria-ssml'));
speechSynthesis.speak(msg);

aria-ssml referencing XML by template ID

<!-- ssml must appear inside a template to be valid -->
<template id="pecan">
<?xml version="1.0"?>
<speak version="1.1"
       xmlns="http://www.w3.org/2001/10/synthesis"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
                   http://www.w3.org/TR/speech-synthesis11/synthesis.xsd"
       xml:lang="en-US">
    You say, <phoneme alphabet="ipa" ph="pɪˈkɑːn">pecan</phoneme>.
    I say, <phoneme alphabet="ipa" ph="ˈpi.kæn">pecan</phoneme>.
</speak>
</template>

<p aria-ssml="#pecan">You say, pecan. I say, pecan.</p>

Client will parse XML and serialize it before passing to a speech API:

var msg = new SpeechSynthesisUtterance();
var xml = document.getElementById('pecan').content.firstElementChild;
msg.text = serialize(xml);
speechSynthesis.speak(msg);

aria-ssml referencing an XML string as script tag

<script id="pecan" type="application/ssml+xml">
<speak version="1.1"
       xmlns="http://www.w3.org/2001/10/synthesis"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
                   http://www.w3.org/TR/speech-synthesis11/synthesis.xsd"
       xml:lang="en-US">
    You say, <phoneme alphabet="ipa" ph="pɪˈkɑːn">pecan</phoneme>.
    I say, <phoneme alphabet="ipa" ph="ˈpi.kæn">pecan</phoneme>.
</speak>
</script>

<p aria-ssml="#pecan">You say, pecan. I say, pecan.</p>

Client will pass the XML string raw to a speech API.

var msg = new SpeechSynthesisUtterance();
msg.text = document.getElementById('pecan').textContent;
speechSynthesis.speak(msg);

aria-ssml referencing an external XML document by URL

<p aria-ssml="http://example.com/pronounce.ssml#pecan">You say, pecan. I say, pecan.</p>

Client will pass the string payload to a speech API.

var msg = new SpeechSynthesisUtterance();
var response = await fetch(el.dataset.ssml)
msg.txt = await response.text();
speechSynthesis.speak(msg);

2.5 Existing Work

2.6 Problems and Limitations

3. Use Case data-ssml

3.1 Background and Current Practice

As an existing attribute, data-* could be used, with some conventions, to include pronunciation content.

3.2 Goal

3.3 Target Audience

Hearing users

3.4 Implementation Options

data-ssml as embedded JSON

When an element with data-ssml is encountered by an SSML-aware AT, the AT should enhance the user interface by processing the referenced SSML content and passing it to the Web Speech API or an external API (e.g., Google's Text to Speech API).

<h2>The Pronunciation of Pecan</h2>
<p><speak>
I say <span data-ssml='{"phoneme":{"ph":"pɪˈkɑːn","alphabet":"ipa"}}'>pecan</span>.
You say <span data-ssml='{"phoneme":{"ph":"ˈpi.kæn","alphabet":"ipa"}}'>pecan</span>.

Client will convert JSON to SSML and pass the XML string a speech API.

var msg = new SpeechSynthesisUtterance();
msg.text = convertJSONtoSSML(element.dataset.ssml);
speechSynthesis.speak(msg);

data-ssml referencing XML by template ID

<!-- ssml must appear inside a template to be valid -->
<template id="pecan">
<?xml version="1.0"?>
<speak version="1.1"
       xmlns="http://www.w3.org/2001/10/synthesis"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
                   http://www.w3.org/TR/speech-synthesis11/synthesis.xsd"
       xml:lang="en-US">
    You say, <phoneme alphabet="ipa" ph="pɪˈkɑːn">pecan</phoneme>.
    I say, <phoneme alphabet="ipa" ph="ˈpi.kæn">pecan</phoneme>.
</speak>
</template>

<p data-ssml="#pecan">You say, pecan. I say, pecan.</p>

Client will parse XML and serialize it before passing to a speech API:

var msg = new SpeechSynthesisUtterance();
var xml = document.getElementById('pecan').content.firstElementChild;
msg.text = serialize(xml);
speechSynthesis.speak(msg);

data-ssml referencing an XML string as script tag

<script id="pecan" type="application/ssml+xml">
<speak version="1.1"
       xmlns="http://www.w3.org/2001/10/synthesis"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
                   http://www.w3.org/TR/speech-synthesis11/synthesis.xsd"
       xml:lang="en-US">
    You say, <phoneme alphabet="ipa" ph="pɪˈkɑːn">pecan</phoneme>.
    I say, <phoneme alphabet="ipa" ph="ˈpi.kæn">pecan</phoneme>.
</speak>
</script>

<p data-ssml="#pecan">You say, pecan. I say, pecan.</p>

Client will pass the XML string raw to a speech API.

var msg = new SpeechSynthesisUtterance();
msg.text = document.getElementById('pecan').textContent;
speechSynthesis.speak(msg);

data-ssml referencing an external XML document by URL

<p data-ssml="http://example.com/pronounce.ssml#pecan">You say, pecan. I say, pecan.</p>

Client will pass the string payload to a speech API.

var msg = new SpeechSynthesisUtterance();
var response = await fetch(el.dataset.ssml)
msg.txt = await response.text();
speechSynthesis.speak(msg);

3.5 Existing Work

3.6 Problems and Limitations

4. Use Case HTML5

4.1 Background and Current Practice

HTML5 includes the XML namespaces for MathML and SVG. So, using either's elements in an HTML5 document is valid. Because SSML's implementation is non-visual in nature, browser implementation could be slow or non-existent without affecting how authors use SSML in HTML. Expansion of HTML5 to include SSML namespace would allow valid use of SSML in the HTML5 document. Browsers would treat the element like any other unknown element, as HTMLUnknownElement.

4.2 Goal

4.3 Target Audience

4.4 Implementation Options

SSML

When an element with data-ssml is encountered by an SSML-aware AT, the AT should enhance the user interface by processing the referenced SSML content and passing it to the Web Speech API or an external API (e.g., Google's Text to Speech API).

<h2>The Pronunciation of Pecan</h2>
  <p><speak>
  You say, <phoneme alphabet="ipa" ph="pɪˈkɑːn">pecan</phoneme>.
  I say, <phoneme alphabet="ipa" ph="ˈpi.kæn">pecan</phoneme>.
</speak></p>

4.5 Existing Work

4.6 Problems and Limitations

SSML is not valid HTML5

5. Use Case Custom Element

5.1 Background and Current Practice

Embed valid SSML in HTML using custom elements registered as ssml-* where * is the actual SSML tag name (except for p which expects the same treatment as an HTML p in HTML layout).

5.2 Goal

Support use of SSML in HTML documents.

5.3 Target Audience

5.4 Implementation Options

ssml-speak: see demo

Only the <ssml-speak> component requires registration. The component code lifts the SSML by getting the innerHTML and removing the ssml- prefix from the interior tags and passing it to the web speech API. The <p> tag from SSML is not given the prefix because we still want to start a semantic paragraph within the content. The other tags used in the example have no semantic meaning. Tags like <em> in HTML could be converted to <emphasis> in SSML. In that case, CSS styles will come from the browser's default styles or the page author.

<ssml-speak>
  Here are <ssml-say-as interpret-as="characters">SSML</ssml-say-as> samples.
  I can pause<ssml-break time="3s"></ssml-break>.
  I can speak in cardinals.
  Your number is <ssml-say-as interpret-as="cardinal">10</ssml-say-as>.
  Or I can speak in ordinals.
  You are <ssml-say-as interpret-as="ordinal">10</ssml-say-as> in line.
  Or I can even speak in digits.
  The digits for ten are <ssml-say-as interpret-as="characters">10</ssml-say-as>.
  I can also substitute phrases, like the <ssml-sub alias="World Wide Web Consortium">W3C</ssml-sub>.
  Finally, I can speak a paragraph with two sentences.
  <p>
    <ssml-s>You say, <ssml-phoneme alphabet="ipa" ph="pɪˈkɑːn">pecan</ssml-phoneme>.</ssml-s>
    <ssml-s>I say, <ssml-phoneme alphabet="ipa" ph="ˈpi.kæn">pecan</ssml-phoneme>.</ssml-s>
  </p>
</ssml-speak>
<template id="ssml-controls">
  <style>
    [role="switch"][aria-checked="true"] :first-child,
    [role="switch"][aria-checked="false"] :last-child {
      background: #000;
      color: #fff;
    }
  </style>
  <slot></slot>
  <p>
    <span id="play">Speak</span>
    <button role="switch" aria-checked="false" aria-labelledby="play">
      <span>on</span>
      <span>off</span>
    </button>
  </p>
</template>
class SSMLSpeak extends HTMLElement {
  constructor() {
    super();
    const template = document.getElementById('ssml-controls');
    const templateContent = template.content;
    this.attachShadow({mode: 'open'})
      .appendChild(templateContent.cloneNode(true));
  }
  connectedCallback() {
    const button = this.shadowRoot.querySelector('[role="switch"][aria-labelledby="play"]')
    const ssml = this.innerHTML.replace(/ssml-/gm, '')
    const msg = new SpeechSynthesisUtterance();
    msg.lang = document.documentElement.lang;
    msg.text = `<speak version="1.1"
      xmlns="http://www.w3.org/2001/10/synthesis"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
        http://www.w3.org/TR/speech-synthesis11/synthesis.xsd"
      xml:lang="${msg.lang}">
    ${ssml}
    </speak>`;
    msg.voice = speechSynthesis.getVoices().find(voice => voice.lang.startsWith(msg.lang));
    msg.onstart = () => button.setAttribute('aria-checked', 'true');
    msg.onend = () => button.setAttribute('aria-checked', 'false');
    button.addEventListener('click', () => speechSynthesis[speechSynthesis.speaking ? 'cancel' : 'speak'](msg))
  }
}

customElements.define('ssml-speak', SSMLSpeak);

5.5 Existing Work

5.6 Problems and Limitations

6. Use Case JSON-LD

6.1 Background and Current Practice

JSON-LD provides an established standard for embedding data in HTML. Unlike other microdata approaches, JSON-LD helps to reuse standardized annotations through external references.

6.2 Goal

Support use of SSML in HTML documents.

6.3 Target Audience

6.4 Implementation Options

JSON-LD

<script type="application/ld+json">
{
  "@context": "http://schema.org/",
  "@id": "/pronunciation#WKRP",
  "@type": "RadioStation",
  "name": ["WKRP",
    "@type": "PronounceableText",
    "textValue": "WKRP",
    "speechToTextMarkup": "SSML",
    "phoneticText": "<speak><say-as interpret-as=\"characters\">WKRP</say-as>"
  ]
}
</script>
<p>
  Do you listen to <span itemscope
    itemtype="http://schema.org/PronounceableText"
    itemid="/pronunciation#WKRP">WKRP</span>?
</p>

6.5 Existing Work

6.6 Problems and Limitations

not an established "type"/published schema

7. Use Case Ruby

7.1 Background and Current Practice

<Ruby> annotations are short runs of text presented alongside base text, primarily used in East Asian typography as a guide for pronunciation or to include other annotations.

ruby guides pronunciation visually. This seems like a natural fit for text-to-speech.

7.2 Goal

7.3 Target Audience

7.4 Implementation Options

ruby with microdata

Microdata can augment the ruby element and its descendants.

<p>
  You say,
  <span itemscope="" itemtype="http://example.org/Pronunciation">
    <ruby itemprop="phoneme" content="pecan">
      pecan
      <rt itemprop="ph">pɪˈkɑːn</rt>
      <meta itemprop="alphabet" content="ipa">
    </ruby>.
  </span>
  I say,
  <span itemscope="" itemtype="http://example.org/Pronunciation">
    <ruby itemprop="phoneme" content="pecan">
      pe
      <rt itemprop="ph">ˈpi</rt>
      can
      <rt itemprop="ph">kæn</rt>
      <meta itemprop="alphabet" content="ipa">
    </ruby>.
  </span>
</p>

7.5 Existing Work

7.6 Problems and Limitations

A. Acknowledgments

This section is non-normative.

The following people contributed to the development of this document.

A.1 Participants active in the Pronunciation TF at the time of publication