Can anyone here tell me how this works? Is the letter of intent binding enough? When is the actual residency contract signed? Any info would be greatly appreciated! Thanks-

I have heard about the pre-match for IMGs and DOs and am wondering how the process works. After you accept, do they give you a contract to sign right away? Is there any way that they can retract it? How is the person accepting the pre-match legally protected? I'd be particulalry interested to hear from people that have actually done this or know details of how the process works. Thanks.