MapKit JS anchorOffset: positive y moves the element up

Apple's docs for mapkit.Annotation anchorOffset say the default anchor is the element's bottom centre, and positive x moves the element left, positive y moves it up (the offset moves the anchor point within the element, the opposite of a CSS translate). So to centre a custom element of height h on its coordinate, use new DOMPoint(0, -h / 2), not +h / 2. If one codebase uses both signs to 'centre' different marks, one of them is wrong: check the docs before trusting either.