One or more of [SSML], [Pronunciation-Lexicon], and [CSS3-Speech] properties has been used to enhance text-to-speech playback quality.


Example 1 — EPUB 3
<meta property="schema:accessibilityFeature">
Example 2 — EPUB 2
<meta name="schema:accessibilityFeature"
Example 3 — Audiobooks
"accessibilityFeature": ["ttsMarkup"]


The ttsMarkup value is used to indicate that a publication's text has been enhanced with additional phonetic markup to improve text-to-speech (TTS) playback.

Synthetic speech engines often struggle to render complex words and heteronyms (words that are spelled the same but sound different). The result is that it can be very difficult for users who cannot see the text to understand what is being read out.

The SSML markup language allows the phonetic renderings of words to be included in the markup of publications to improve rendering, for example. PLS pronunciation lexicons similarly allow libraries of phonetic pronunciations to be attached to HTML content.

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