Use of semicolon in vertical text flow isn't well defined, so most fonts don't include vertical form for semicolon, so they appear in upright in existing systems. JLTF believes it's simply because no one expects authors to use semicolons in vertical text flow, but it doesn't stand anymore when readers can change text flow.
- readers can choose the orientation therefore we need to settle the handling of colon in vertical text
An alternative approach:
- readers can choose the orientation therefore we need to be able to record in documents different text for horizontal and vertical presentations
Clearly, most of the text will be the same in both orientations, so the alternate versions need to be local.
Such machinery seems to be needed for
In vertical writing mode, symbols for units are usually described with katakana (cl-16), such as センチメートル (centimeter) or センチ(abbreviation of centimeter in katakana, "senchi"). In horizontal writing mode, the International System of Units (SI) is usually used, such as "cm".
Something like "<orientationalternate><horizontal>cm</horizontal><vertical>センチ</vertical></orientationalternate>"
(I hope we will not spend month discussing whether the <horizontal> is really needed :lol:)
Of course, we still need to settle the colon somehow.