in h3_bbox.c [72:80]
bool bboxContains(const BBox *bbox, const LatLng *point) {
return point->lat >= bbox->south && point->lat <= bbox->north &&
(bboxIsTransmeridian(bbox) ?
// transmeridian case
(point->lng >= bbox->west || point->lng <= bbox->east)
:
// standard case
(point->lng >= bbox->west && point->lng <= bbox->east));
}