layerVariances in samples/sampleUffSSD/config.py

Hello,

can someone help me understand what layerVariances is in config.py

PriorBox = gs.create_node("PriorBox",
    numLayers=6,
    minScale=0.2,
    maxScale=0.95,
    aspectRatios=[1.0, 2.0, 0.5, 3.0, 0.33],
    layerVariances=[0.1,0.1,0.2,0.2],
    featureMapShapes=[19, 10, 5, 3, 2, 1])

I understand featureMapShapes[19,10,5,3,2,1] are the side lengths of five feature maps,
which are from InceptionV2 and SSD.

Thank you.