W3C Invites Implementations of IMSC Text Profile 1.3

The Timed Text Working Group has published IMSC Text Profile 1.3 as a W3C Candidate Recommendation Snapshot. IMSC 1.3 defines a text-only profile of [ttml2] intended for subtitle and caption delivery applications worldwide. It improves on IMSC 1.2 Text Profile by adding support for superscript and subscript text, and provides authoring guidelines for the Japanese language. The IMSC 1.2 Image Profile is not reproduced within IMSC 1.3, and the IMSC Hypothetical Render Model [imsc-hrm] is now a separate Recommendation, referenced by IMSC 1.3. 

Comments are welcome via Github issues or email to public-tt@w3.org by 15 January 2026.