"begin with the recto side as"?

I am not sure if the following part is a right way of describing books in vertical writing: "vertical writing mode whose books…". someone? perhaps just simply "books in vertical writing"?

I am not sure if the following part is a right way of describing books in vertical writing: "vertical writing mode whose books…". someone? perhaps just simply "books in vertical writing"?

actually, wondered something like that, since Japanese text is 縦組の右綴じの場合 but not 縦組で右綴じの場合.
but writing as books in vertical writing lacks a note on right side bounded,, so books in vertical writing mode and bounded on the right-hand side or something??

"books in vertical writing direction which are bounded on the right-hand side" ?

You could use 'vertically set books'. My suggestion:

Books usually begin with the recto side as page one. Accordingly, vertically set books, which are bound on the right-hand side, begin with the left page in a spread (see [[[#fig3_1_11]]]), whereas horizontally set books, which are bound on the left-hand side, begin with the right page in the spread.

You could use 'vertically set books'. My suggestion:

looking around in JLReq document, there was an use case of vertically set books often have indexes in horizontal writing mode and also section 2.2.3-a uses vertically set in similar context as vertically set Japanese documents are bound on the right-hand side. So, let me use this. (also will check other uses.)

@kidayasuo @r12a let me re-request your review on 22685c1, using vertically set books.

@himorin looks good to me, except that [1] there are a couple of index pointers in the Japanese that are not in the English version (in fact that also applies to the previous, unchanged paragraph), and [2] i wonder whether the Japanese version needs further clarifications (just asking).

for 1), yes, I noticed that by your comment, and willing to update (as 96f0b99).
for 2) on the original target text, I think current Japanese text is sufficient.