[css-writing-modes] Vertical upright Mongolian intrinsic orientation

Hi,

I’m trying to figure out what is the correct way to render traditional
Mongolian text in upright text-orientation.

The Writing Modes 3 spec says: “Typographic character units from vertical
scripts are typeset with their intrinsic orientation” [1].

Mongolian is listed as a vertical script with a vertical intrinsic
direction (ttb) [2].

Here’s my test case: https://jsfiddle.net/9o1wazj2

I tried it in Chrome55 and Firefox50 on Mac/Windows10 (on Mac 10.12, the
default font didn’t display any text orientation correctly, so I had to
install the Mongolian White font [3]).

The mixed and sideways Mongolian texts are rendered correctly, but the
upright text isn’t. Does it mean that browsers are typesetting Mongolian
upright text wrong?

Regards,
Kari

[1] https://www.w3.org/TR/css-writing-modes-3/#text-orientation
[2] https://www.w3.org/TR/css-writing-modes-3/#script-orientations
[3] http://www.mongolfont.com/en/font/mnglwhiteaat.html