An Obama administration fact sheet on the deal says only that Iran will be able to conduct “limited research and development” into the centrifuges — which are far more efficient than the relatively crude devices Iran now operates — “according to a schedule and parameters which have been agreed to” by Iran, the United States, and five other world powers.

Although Iran will be barred for a decade from enriching uranium with the advanced devices, that schedule and those parameters remain otherwise unknown.

Critics of the agreement were quick to zero in on the question. “This is a bad framework that will lead to a bad and dangerous deal,” said an Israeli government source in Jerusalem, who cited as a key complaint the fact that Iran “will continue its centrifuge research and development.”

The research-and-development question is just one of a handful of key issues left unresolved, at least in public, and which could endanger the agreement’s survival.