Question about PCIe output reference clock for Controller Number mapping

Question about PCIe controller # mapping.

In Jetson_AGX_Orin_Series_Design_Guide_DG-10653-001_v1.2.pdf, “PCIe output Reference clock for controller #xxx” is described.

How can I match PCIe vs PCIe controller #xxx?

Where can I refer to the document that described this?