question on WS-BaseFaults

For implementation purposes, I'd like to know whether all faults thrown
by operations in a WS-Resource WSDL are required to be base faults (i.e.
types that extend BaseFault), or whether other forms of soap faults may
also be used. After reading the Nov 04 draft of the WSRF-BF spec, I am
still unsure. Section 3 (Use of Base Faults in WSDL) seems like it might
be suggesting that all faults must be base faults, but it's not clear.
Can someone please clarify?

Thank you.
Ian