Mongolian characters incorrectly rotated and not joining in vertical text

[r12a]

This issue is applicable to Traditional Mongolian.

Lines of text in the Traditional Mongolian script run vertically from top to bottom of the page. Lines flow from left to right. The script is cursive, meaning that the characters join along the vertical centre line. Here is an example:

Note the orientation of the glyphs.

Specs:
css-writing-modes-4 provides the writing-modes property. The vertical-lr value is designed to display Traditional Mongolian text as expected.

Tests & results:
i18n test suite, Vertical text, Vertical-LR, Glyphs

• Gecko: ✅ Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:100.0) Gecko/20100101 Firefox/100.0

• Blink: ✅ Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/101.0.4951.54 Safari/537.36

• WebKit: ❌ Rotates lines appropriately, but doesn't display characters in the correct orientation and doesn't join them up (see the left-hand line below). Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.4 Safari/605.1.15

  

  To get this to work in WebKit you need to add text-orientation: sideways to the CSS, which should not be necessary, and is not needed for Gecko and Blink browsers.

Browser bug reports:
Webkit

Priority:
This issue makes it impossible to use Traditional Mongolian on WebKit-based browsers. The priority for Web users is being marked as basic because other browsers are available.

[r12a]

The first comment in this issue contains text that will automatically appear in one or more gap-analysis documents as a subsection with the same title as this issue. Any edits made to that comment will be immediately available in the document. Proposals for changes or discussion of the content can be made in comments below this point.

Relevant gap analysis documents include:
Mongolian

[r12a]

Updated the format of the gap report, and raised a bug report against WebKit.