The contingent or smart orders are implemented by brokers (E*Trade’s are different from Interactive Brokers) or in trading platforms. They are held outside the exchange until whatever trigger condition allows them to be expressed as an order directly supported (which introduces timing and other risks that they won’t work like a natively exchange-supported order).

In terms of links, I don’t have a ready primer to vouch for. I worked 6 years in online broker tech, but it was decades ago.