Platform/Features/Vertical text

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Vertical text
Stage Draft
Status `
Release target `
Health OK
Status note `


Product manager Jet Villegas
Directly Responsible Individual `
Lead engineer Simon Montagu
Security lead `
Privacy lead `
Localization lead `
Accessibility lead `
QA lead `
UX lead `
Product marketing lead `
Operations lead `
Additional members `

Open issues/risks

Specification is in flux.

Stage 1: Definition

1. Feature overview

Add support for vertical text layout.

Text for most scripts on the web today are laid out horizontally. However, Japanese, Chinese and to some degree Korean can also be laid out vertically. When laid out vertically, these languages use top-to-bottom, right-to-left flows. Classical Mongolian is generally considered a "vertical only" language, although in multi-script contexts it can also be drawn horizontally. Mongolian, along with Phags-pa flows top-to-bottom, left-to-right. Western text such as Latin, Greek and Cyrillic can also be displayed vertically, examples of this often appear on book spines and in signage.

2. Users & use cases

Users: publishers of vertically typeset content (e-publishing organisations, independent web authors, especially in East Asia)

Example use cases:

  • Web-based e-readers for Japanese novels (especially on mobile devices)
  • Web pages that use classical Mongolian script

3. Dependencies


4. Requirements

  • Support vertical text for whole documents (i.e. initial containing block uses a vertical writing mode) and document fragments (i.e. orthogonal flows)
  • Support both top-to-bottom, right-to-left (e.g. CJK) and top-to-bottom, left-to-right (e.g. Mongolian) writing modes.
  • As far as possible (particularly given that the spec is in flux), conform to the relevant parts of CSS3 Writing Modes specification—most likely the writing-mode and text-orientation properties.


  • Support all of the CSS Writing Modes specification
    • For example, properties such as unicode-bidi, text-combine-horizontal, and text-combine-mode are probably outside the scope of this feature
  • Support HTML ruby
  • Support vertical text in SVG

Stage 2: Design

5. Functional specification

  • Bug 0 - Prototype
  • Bug 1 - Parse writing mode and text-orientation
  • Bug 2 - Logicalize Reflow APIs
  • Bug 3 - Logicalize Reflow for all frame classes
  • Bug 4 - Refactor and extend logical CSS properties
  • Bug 4 - Orthogonal Flows
  • Bug 5 - UI
  • Bug 6 - Text/Glyph Layout

6. User experience design


Stage 3: Planning

7. Implementation plan

  • Prototype of a vertical text layout. This will include:
    • logicalization of a minimum of frame types
    • layout of a minimum of frame types
    • Glyph layout of CJK only
    • Parsing, orthogonal flows and UI will not be included
  • Bug 2: Parsing of writing-mode and text-orientation
    (see Implementation below)

The above is done. Steps to implement (parallelizable steps preceded by --> to indicate possible forking-off):

  • --> Bug 4 - Refactor existing logical CSS properties
  • Bug 1 - Parse writing mode and text-orientation
  • --> Extend logical CSS properties to handle vertical text (depends only on Bugs 1 and 4)
  • Bug 2: Logicalization of layout parameters
    • May involve some renaming across the layout engine, but shouldn't affect logic at this point
    • Note that some frame classes will continue to be physical, e.g. images, even after full logicalization
  • Bug 3: Logicalize Block and Inline layout
    • Logicalize nsBlockFrame. Get vertical-only/horizontal-only documents consisting of only block frames working/tested
    • Note that not all properties get treated the same. For example, the offset of a text-shadow property is unaffected by writing mode.
    • Logicalize nsLineLayout, nsInlineFrame, nsTextFrame, etc. Get inline layout working for vertical-only documents. Make the text just draw sideways for now.
  • --> After block and inline layout, other frame classes can be converted set by set, e.g.
    • Tables
    • Flexbox
    • etc.
  • --> Bug 4: Orthogonal flows
    • Probably requires a lot of rework of intrinsic sizing. This is a complicated task!
  • --> Bug 5: UI features
    • scrollbars
    • mapping scrollwheel
    • vertical text selection
    • vertical text selection cursor
    • caret browsing
    • list boxes/combo boxes (initial implementation should just transform the control; next pass does actual vertical layout)
    • menus
    • other?
  • --> Bug 6: Glyph orientation
    • Using character properties such as those defined in UTR-50 (currently under review)
    • Supporting different modes as necessary (e.g. stacked vs default, cf. text-orientation which is in flux)
    • Glyph selection—choosing vertical variants, using vertical metrics
    • OpenType model for vertical text needs to be flushed out a bit more (e.g. which features are on by default in the vertical case?)

8. Reviews

Security review


Privacy review


Localization review




Quality Assurance review


Operations review


Stage 4: Development

9. Implementation

Main bugzilla entry

  • Need to investigate how to pref CSS keyword parsing (and all writing-mode processing) on and off. (This is relatively straightforward, now that bug 753522 is implemented. Just specify the pref in the property's chunk of nsCSSPropList.h, and use Preferences::GetBool() elsewhere if necessary.)
  • Possibly want to be able to #ifdef it as well? Or just back out the changes after each uplift so we don't pay the perf cost until it's ready? [There shouldn't be any perf cost.]
  • Multi-column vertical layout
  • Form controls
  • Tables
  • (Probably lots of other HTML elements that require special handling? e.g. list markers. Presumably images don't rotate (i.e. width/height are physical) but form controls do?)
  • Pagination
  • Implement min/max/fit-content, fill-available

Stage 5: Release

10. Landing criteria


Feature details

Priority Unprioritized
Rank 999
Theme / Goal `
Roadmap Platform
Secondary roadmap `
Feature list `
Project `
Engineering team Layout

Team status notes

  status notes
Products ` `
Engineering ` `
Security ` `
Privacy ` `
Localization ` `
Accessibility ` `
Quality assurance ` `
User experience ` `
Product marketing ` `
Operations ` `