WPT details: This is part of Interop 2023 and is covered by tests under "wpt/css/css-masking": https://wpt.fyi/results/css/css-masking?label=experimental&label=master&product=chrome&product=firefox&product=safari&aligned&view=interop&q=label%3Ainterop-2023-cssmasking
Support the xywh() and rect() values on clip-path, which make it easier to specify rectangular or rounded-rectangular clips.