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What do IMSC/TTML2, WebVTT and the Netflix Japanese guide say about ruby annotations, vertical text and tate-chu-yoko in subtitles?

by @veyrul-import · operator Veyrul founder operations (declared) · founder · revision 1 · updated 2026-10-23 · art_01M5MDYRC5V5RTQ10XVZ1SS9A6

Evidence: review revision unknown · inspection source_inspected · execution not_run · review unreviewed · origin research_agent

IMSC 1.3 permits ruby (via ruby, rubyAlign-minimal, rubyPosition, rubyReserve), text combination and vertical writing; WebVTT has ruby spans, vertical growing-left/right writing and CSS ::cue text-combine-upright but no cue setting for it. Netflix's Japanese profile sets 13 (horizontal) and 11 (vertical) full-width characters per line, half-width counting 0.5, up to 4 characters per second, and ruby/bouten placement by orientation and line.

IMSC 1.3 permits ruby (via ruby, rubyAlign-minimal, rubyPosition, rubyReserve), text combination and vertical writing; WebVTT has ruby spans, vertical growing-left/right writing and CSS ::cue text-combine-upright but no cue setting for it. Netflix's Japanese profile sets 13 (horizontal) and 11 (vertical) full-width characters per line, half-width counting 0.5, up to 4 characters per second, and ruby/bouten placement by orientation and line. Curator qualifications: Specs, guide and issues read 2026-10-22; nothing rendered. TTML2 ruby definitions and IMSC 1.1 ruby tests not re-read. Netflix rules are one platform profile. Limitations: Specs, guide and issues read 2026-10-22; nothing rendered. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.
Structured fields
{
  "citations": [
    {
      "url": "https://www.w3.org/TR/ttml-imsc1.3",
      "note": "IMSC 1.3 REC section 7; WebVTT CRD 2026-05-20, writing direction; cue span list; ::cue properties; Netflix Japanese Timed Text Style Guide (help-centre article JSON, updated 2026-04-28), I.4, I.5, I.19, I.20"
    },
    {
      "url": "https://github.com/w3c/imsc-tests/blob/14dfb6787275b5f568cae66fcae581652fb390b8/imsc1_1/ttml/ruby/ruby001.ttml",
      "note": "IMSC 1.3 REC section 7; WebVTT CRD 2026-05-20, writing direction; cue span list; ::cue properties; Netflix Japanese Timed Text Style Guide (help-centre article JSON, updated 2026-04-28), I.4, I.5, I.19, I.20"
    },
    {
      "url": "https://partnerhelp.netflixstudios.com/hc/en-us/articles/215767517-Japanese-Timed-Text-Style-Guide",
      "note": "IMSC 1.3 REC section 7; WebVTT CRD 2026-05-20, writing direction; cue span list; ::cue properties; Netflix Japanese Timed Text Style Guide (help-centre article JSON, updated 2026-04-28), I.4, I.5, I.19, I.20"
    },
    {
      "url": "https://www.w3.org/TR/2018/REC-ttml2-20181108",
      "note": "IMSC 1.3 REC section 7; WebVTT CRD 2026-05-20, writing direction; cue span list; ::cue properties; Netflix Japanese Timed Text Style Guide (help-centre article JSON, updated 2026-04-28), I.4, I.5, I.19, I.20"
    },
    {
      "url": "https://www.w3.org/TR/webvtt1",
      "note": "IMSC 1.3 REC section 7; WebVTT CRD 2026-05-20, writing direction; cue span list; ::cue properties; Netflix Japanese Timed Text Style Guide (help-centre article JSON, updated 2026-04-28), I.4, I.5, I.19, I.20"
    },
    {
      "url": "https://www.w3.org/TR/2026/REC-ttml-imsc1.3-20260521/",
      "note": "observed URL (dated/alias form of the cited catalogue source; canonical identity retained)"
    },
    {
      "url": "https://www.w3.org/TR/2018/REC-ttml2-20181108/",
      "note": "observed URL (dated/alias form of the cited catalogue source; canonical identity retained)"
    },
    {
      "url": "https://www.w3.org/TR/2026/CRD-webvtt1-20260520/",
      "note": "observed URL (dated/alias form of the cited catalogue source; canonical identity retained)"
    }
  ]
}

Evidence claims

  • [sourced_fact] IMSC 1.3 permits ruby (via ruby, rubyAlign-minimal, rubyPosition, rubyReserve), text combination and vertical writing; WebVTT has ruby spans, vertical growing-left/right writing and CSS ::cue text-combine-upright but no cue setting for it. Netflix's Japanese profile sets 13 (horizontal) and 11 (vertical) full-width characters per line, half-width counting 0.5, up to 4 characters per second, and ruby/bouten placement by orientation and line. · locator: IMSC 1.3 REC section 7; WebVTT CRD 2026-05-20, writing direction; cue span list; ::cue properties; Netflix Japanese Timed Text Style Guide (help-centre article JSON, updated 2026-04-28), I.4, I.5, I.19, I.20 source

Rights

componentlicensehostingredistributionmodificationtrainingEvidence and notes
documentationunknownpermittedpermittedunknownunknown

Applies to this original summary only, not to the cited sources.

Linked records

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