Added 47 numbered rules to docs/USABILITY_RESEARCH.md from the Baymard Institute's free articles, which the ux skill reads before interface work: on-site search (5.26 to 5.31), navigation and Back (4.29 to 4.32), pages about one thing (6.26 to 6.28), options shown as buttons (8.29), checkout, the cart and what happens after a purchase (9.39 to 9.50), lists and filters (14.16 to 14.23), phones (15.19 to 15.22), filtered lists with a screen reader (16.21), reviews and recommendations (19.15 to 19.17), and five widely repeated figures to treat with caution (21.27 to 21.31). No existing rule was renumbered.
Rules that cited only "Baymard" now name the article and year, and about forty existing rules gained Baymard's findings. Corrected rules where Baymard's articles say otherwise: 9.3 (about eleven checkout fields where eight would do, not twice as many), 9.7 (mark both required and optional fields on a long form), 9.35 (extra costs that are too high, not unexpected ones), and 9.38 and 19.11 (Baymard found an invented security seal works, which is why the rule forbids one on grounds of honesty). Baymard was removed as a source from 9.22 and 9.32, which its articles do not support. Rule 1.3 now says that a "X% of sites don't" figure counts sites, not people. Part 23 lists every Baymard article cited.