Background class ID in VOC data

[vodp]

I see from the code that background_class_id is assigned to zero. However in the file https://github.com/tanakataiki/ssd_kerasV2/blob/master/get_data_from_XML.py the zero-th class index is assigned to Aeroplane class. How should I understand this?

[tanakataiki]

back ground is added all the time without considering it when training so you dont have to change it, that is why I think background is unneccesary in making pkl