The CPCI-S specifies a ±10% margin for the 12V, while FMC only allows ±5%. Since the system boards will generally pass the 12V directly to the mezzanine, we might want to consider adding a clause in the DI/OT specs to apply a ±5% margin to the 12V, deviating from the more relaxed CPCI-S specifications. That way we don't lose compatibility with any (hypothetical) FMC-compliant communication mezzanines that might need the tight margins.