Fixed Format EPUB all seem to fail WCAG 2.1 SC 1.4.10

Dear Community Group,
While I was looking at the EPUB Content Document 3.2 from the W3C Community Group I could not help but notice that there is no case to cover 320 CSS Pixels in width. Support for this case is now required (normative) by WCAG 2..1 in recognition of the fact that horizontal scrolling does not support effective reading.

For an easy visualization of this issue you may look at, https://nosetothepage.org/Fitz/2dScroll.html. This presentation is good for sighted readers because our best examples are visual. If a blind user would like to experience the issue imagine a braille document where each line of text was laid out across two pages, a left and right page. To read a line of text, you would start on the left page and then move to the right page; find the remainder of the line to read on the right page; finish reading the line on the right page and then find the next line on the left page. This is how people with low vision have been expected to read forever. To read a 100 page book requires 10,000 such transitions from page to page, at a minimum. Note: When I say minimum I mean the minimum number of scrolls needed for the user to have an opportunity to see each letter once.  In recognition of this difficulty the W3C developed the Reflow success criterion (SC 1.4.10). This severe problem for people with partial sight was trivialize by the Blind and Visual Impairment support community for many years, and it probably cost many young people the opportunity to attend and / or complete college.

I personally worked my way through a graduate program in mathematics using technologies that required horizontal scrolling. The only thing that got me through was my deep love of the subject. At that time we could not even get recorded books for the blind, since the Chafee amendment had not passed.

In my 30 years as a Professor of computer science I taught around 2400 CS majors. In that time 2 students with partial sight graduated from our program. Give 3,000,000 people with partial sight in the US that is a profoundly low level of under representation. Fixed Format explains a lot of that.

Sincerely, Wayne