Interaction of "zoom content" and vertical writing modes

The latest version of the "zoom content" proposal specifies that "content can be presented at a width equivalent to 320 CSS pixels...". In the case of a vertical writing mode, however, it seems that the proposal would not prevent a user with low vision who enlarges the text within appropriate limits from having to engage in vertical scrolling to read the lines.
I'm not familiar with the details of how vertical scripts are used, but if the whole or a significant portion of a page is presented in such a writing mode, then the current version of "zoom content" doesn't appear to address the needs of low vision users of such writing systems.
If this issue doesn't have a straightforward answer, I can open it formally on GitHub.


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