Key differences: * new Text profile designator * `tts:fontVariant` permitted, with values `normal`, `sub` and `sup` permitted. The derivation for `tts:fontVariant` suggests that the approach described in [CSS Fonts Level 3](https://www.w3.org/TR/2018/REC-css-fonts-3-20180920/#font-variant-position-prop) would be appropriate.
Key differences:
tts:fontVariantpermitted, with valuesnormal,subandsuppermitted.The derivation for
tts:fontVariantsuggests that the approach described in CSS Fonts Level 3 would be appropriate.