WPT details: https://wpt.live/css/css-overflow/inheritance.html https://wpt.live/css/css-overflow/logical-overflow-001.html https://wpt.live/css/css-overflow/parsing/overflow-computed.html https://wpt.live/css/css-overflow/parsing/overflow-invalid.html https://wpt.live/css/css-overflow/parsing/overflow-valid.html
The overflow-inline and overflow-block CSS properties allow setting overflow in inline and block direction relative to the writing-mode. In a horizontal writing-mode overflow-inline maps to overflow-x, while in a vertical writing-mode it maps to overflow-y.
Without the logical variants of overflow the author needs to know whether the writing-mode is horizontal or vertical and set overflow-x or overflow-y based on that knowledge. The logical variants lets the author make the overflow directions respond to the writing-mode.