[1] 次の CSS特性があります。

nav-index
nav-up
nav-down
nav-left
nav-right

[2] tabindex, 空間ナビゲーションも参照。

[3] [css-ui-3] Marked the nav-* properties at risk (frivoal著, 2017-01-26 18:03:51 +09:00) https://github.com/w3c/csswg-drafts/commit/5b6377999ca0fd7e8dc1c02d7ea10b3ed6f175cc

[4] [css-ui] Move nav-* from l3 to l4 (frivoal著, 2017-08-10 21:36:58 +09:00) https://github.com/w3c/csswg-drafts/commit/4e5fae039a49f84e614884a83f7963273f964e2e