Maybe already answered but a few comments to questions from Jens:
2020年12月5日(土) 6:08 Jens Tröger <jens.troeger@light-speed.de>:
>
> And how does the `dir` global attribute fit in:
>
> https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/dir
`dir` and `writing-mode` are similar to determine text flow, but are
different in that:
1. The `dir` is semantic for bidirectional languages, hence it is
defined in HTML. There is no, for example, Arabic in LTR.
2. Vertical text flow is a stylish choice. A content can be styled
either in horizontal or vertical. Hence it is defined in CSS.
And isn’t the writing direction implied by the language attribute (assuming
> metadata & content is marked correctly):
>
>
> https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/lang
As above, the default `dir` can be computed from `lang`, but `writing-mode`
is up to authors.