The Type I superluminous supernova catalogue – II. Spectroscopic evolution in the photospheric phase, velocity measurements, and constraints on diversity. - Aamer, Aysha; Nicholl, Matt; Gomez, Sebastian; Berger, Edo; Blanchard, Peter; Anderson, Joseph P; Angus, Charlotte; Aryan, Amar; Ashall, Chris; Chen, Ting-Wan; Dimitriadis, Georgios; Galbany, Lluís; et al. (Monthly Notices of the Royal Astronomical Society, 2025)