Why in nn.conv2d, the padding can be a four dimension tuple?

Before the relay.build, I print the Relay IR Module, but I find that:

nn.conv2d(%data, %graph_conv_weight, strides=[2, 2], padding=[1, 1, 1, 1], channels=32, kernel_size=[3, 3])

Can anyone help me to point out the direction in padding tuples? For example, padding[0] represents the height_top?

Appears to be [top, left, down, right]

thank you very much@AndrewZhaoLuo