Function round_rect_radii 

pub(super) fn round_rect_radii(
    radii: &UnrestrictedDoubleOrDOMPointInitOrUnrestrictedDoubleOrDOMPointInitSequence,
) -> Vec<RoundRectRadius>

Part of step 5 of https://html.spec.whatwg.org/multipage/#dom-context-2d-roundrect Validation is done later as order of operations matter.