[css-text-decor] Orientation of emphasis marks for sideways text

The current spec says:
Marks must remain upright in vertical writing modes: like CJK
characters, they do not rotate to match the writing mode.

There is a question that, should the emphasis marks remain upright
even when using sideways-* writing modes or specifying sideways
orientation?

This should be clarified in the spec whatever the answer is.

- Xidorn