#1122: WG Revision: IMSC 1.3 (minor revision to IMSC 1.2)

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Opened Jul 17, 2025

Specification

https://www.w3.org/TR/2025/WD-ttml-imsc1.3-20250722/

Explainer

No response

Links

The WG's request for this TAG review: https://www.w3.org/2025/07/17-tt-minutes.html

TAG review of the previous version of this specification, if any: https://github.com/w3ctag/design-reviews/issues/474

A description of what has changed since our previous review: https://www.w3.org/TR/2025/WD-ttml-imsc1.3-20250722/#changes

  • Japanese character set

A recommended supplementary character set for the Japanese language has been added based on feedback from ARIB, which is an organization of Japanese users.

https://github.com/w3c/imsc/issues/544

  • Superscript/subscript text

Support for superscript/subscript text was added based on feedback from French users. This is merely permitting a feature that has been part of TTML2, of which IMSC is a profile, since its inception.

https://github.com/w3c/imsc/issues/583

  • Image profile

The Image Profile specified in earlier versions of this specification is removed, following a survey of IMSC users.

https://github.com/w3c/imsc/issues/600

  • Hypothetical Render Model

Following publication of the (IMSC Hypothetical Render Model)[https://www.w3.org/TR/imsc-hrm/] as a separate REC, the definition of the Hypothetical Render Model is removed from this document and replaced with a reference to the separate REC.

https://github.com/w3c/imsc/issues/582

The specification

Where and by whom is the work is being done?

  • GitHub repo: https://github.com/w3c/imsc
  • Primary contacts:
    • @palemieux (editor)
    • @nigelmegitt (WG co-chair)
    • @gkatsev (WG co-chair)
    • @himorin (Team contact)
  • Organization/project driving the specification: TTWG

Feedback so far

No response

You should also know that...

Review requested no later than Sunday, October 19 2025, given the narrow range of changes.

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Discussions

Comment by @lolaodelola Jul 23, 2025 (See Github)

Hi @palemieux,

Thanks for seeking review. This review will be better conducted by I18-N since it's purely about character sets. We don't see any architectural implications of IMSC 1.3 so we'll close this issue.