code: def _within_box(points, boxes):
      
      x_within = (points[..., 0] >= boxes[:, 0, None]) & (
          points[..., 0] <= boxes[:, 2, None]
      )
      y_within = (points[..., 1] >= boxes[:, 1, None]) & (
          points[..., 1] <= boxes[:, 3, None]
      )
      return x_within & y_within
docs: Validate which keypoints are contained inside a given box.
      points: NxKx2
      boxes: Nx4
      output: NxK