> This module specifies the text layout model in CSS and the properties that control it. It covers bidirectional and vertical text.
There have been numerous revisions in the subsequent years. In 2017 w3.org published this article specifically on using vertical text in paragraphs, forms, lists and tables: https://www.w3.org/International/articles/vertical-text/
Perhaps not HTML itself, but the first draft for writing modes in CSS is over 10 years old: https://www.w3.org/TR/2010/WD-css3-writing-modes-20101202/
> This module specifies the text layout model in CSS and the properties that control it. It covers bidirectional and vertical text.
There have been numerous revisions in the subsequent years. In 2017 w3.org published this article specifically on using vertical text in paragraphs, forms, lists and tables: https://www.w3.org/International/articles/vertical-text/