Contingency Sale?

When we bought our second house, we did a contingency sale. Meaning we had to sell our first house then would be free to buy the second. This was done courtesy of our realtor (for a fee of course). Does anyone know where, on the sales contract, that you would put that in? I didn't see it in those words, but would like to know where to look for it in the event we sell this one. I also want to know just in case we look at a contract from a buyer that might put it in their contract. You know, the whole knowledge is power thing... Hope you are all well. Good luck Saturday.