The sliding panels for "about this item", "rights", and "index" use the HTML landmark <aside>.
However, aside needs to be at the top level, rather than inside main.
Impact: moderate
https://www.w3.org/WAI/ARIA/apg/practices/landmark-regions/
https://www.accessibilitychecker.org/wcag-guides/ensure-the-complementary-landmark-or-aside-is-at-the-top-level/