Milgrom's proposed design was adopted in large part by the commission. Called the simultaneous multiple round (SMR) auction, this design introduced several new features, mostly importantly an "activity rule" to ensure active bidding. Milgrom and Weber developed an activity rule to accompany their simultaneous closing rule to ensure that bidders could not hold back while observing the bids of others. The activity rule required that bidders maintain a certain level of activity, either by being the current high bidder or by submitting a new bid, in each round or else forfeit all or part of its eligibility to submit bids in future rounds. "Milgrom and Weber developed this insight into the activity rule that the FCC has used in all its simultaneous multiple round auctions. The Milgrom-Wilson activity rule was an elegant, novel solution to a difficult practical auction design issue." Activity rules are now a nearly universal feature in dynamic multi-item auctions.