How to understand the line-nms?

I find that the line-nms delete some boxes.  It seems a little confusing. The left-top and right-top point are used as left-top and right-bottom point , respectively. The x-coordinate of left-bottom point is used as confidence. It is a little difficult to understand it.

https://github.com/YCG09/chinese_ocr/blob/9af64905f7e1a226d902feac5c0dfd64399ce6b2/ctpn/lib/text_connector/detectors.py#L42
