Upright text orientation not supported — FIXED !
This issue is applicable to Chinese, Japanese, Korean, and Mongolian.
By default, in runs of Latin alphanumeric text the letters are rotated 90º and run down the page. However, in some instances the alphanumerics need to stand upright. For example, this is important for acronyms.

Browsers need to allow content authors to indicate where alphanumerics should be rendered upright.
The GAP
writing-modes The CSS text-orientation property has a value upright which is meant to produce this behaviour, but not all browsers support it.
Priority
Upright-oriented Latin text, especially, is used commonly for acronyms in Chinese, Japanese, Korean, & Mongolian vertical text, so this is a significant gap for general web content.
Tests & results
Interactive test, text-orientation:upright will make Latin characters and digits sit upright in vertical text.
Action taken
Outcomes
All major browser engines now support this feature!
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: Chinese • Japanese • Korean • Mongolian