As agreed at https://www.w3.org/2019/10/10-tt-minutes.html#x03 request HR of TTML2:

• accessibility - https://lists.w3.org/Archives/Public/public-tt/2019Oct/0039.html
• internationalization - https://lists.w3.org/Archives/Public/public-tt/2019Oct/0037.html
• performance
• privacy - https://lists.w3.org/Archives/Public/public-tt/2019Oct/0038.html
• security - https://lists.w3.org/Archives/Public/public-tt/2019Oct/0038.html
• TAG - Timed Text Markup Language (TTML2) 2nd Edition w3ctag/design-reviews#432