In the Display techniques for ONIX document - propose to add the text-to-speech hinting provided (ONIX Code 21 from list 196) to the Additional accessibility information - clarity section.
CROSSWALK - https://w3c.github.io/a11y-discov-vocab/crosswalk/
schema.org ttsMarkup already mapped to ONIX codes 21 - Text-to-speech hinting provided and code 22 - Language tagging provided from list 196
In the Display techniques for ONIX document - propose to add the text-to-speech hinting provided (ONIX Code 21 from list 196) to the Additional accessibility information - clarity section.