1 - all back-ends: fail on non-zero domain
7 - extend the register table
9 Capabilities with partial decoding:
10 - PCIe 2nd set of control/status registers (have spec)
11 - HyperTransport caps (have spec)
13 Capabilities with no decoding:
15 - CompactPCI central resource control
18 - Power Budgeting (ext'd, needs write access to enumerate)
19 - Root Complex * (ext'd)
20 - Multi-Function Virtual Channel (ext'd)
21 - Root Bridge Control Block (ext'd)