VI_ATTR_FIND_RSRC_MODE documentation?

I have a PXI chassis. By running NI-MAX and tracing with NI-IOTRACE I can see that MAX calls viSetAttribute(session, VI_ATTR_FIND_RSRC_MODE, 0x8018) as the first order of business; subsequently, it can enumerate all the PXI slots with viFindRsrc("/?*") - i.e. viFindNext returns all the PXI*::INSTR resources. Without setting that attribute, I can only find PXI*::BACKPLANE. I can't find any documentation for this attribute.

Please indicate where I can find documentation for this attribute, as I'd like to enumerate PXI slots.