Quote from jimrockford:
The whole rule!
Maybe if you can tell us which part of Rule 72 you don't understand, I'll have time to clarify it. I certainly don't have time to explain the whole rule.
Summary of Rule 72: priority of bids and offers, at the same price on NYSE, is NOT based on time. It is based instead on a very complicated set of rules, set forth in Rule 72.
Note: public limit orders on the specialist's public limit order book do compete with each other in a strict price-time priority, but they do not receive price-time priority against bids and offers from floor brokers. They compete with floor brokers according to the scheme set forth by Rule 72. Note also that
the procedures actually followed deviate somewhat from Rule 72, as was explained by our former specialist friend, cstu.