spring rush

I am considering participating in Spring Rush next semester. The Panhellenic website has very little to no information on it, except that it is not a formal process. I know the sororities that participate are different every year, but is there anyone who knows what the process is like. Like do the houses participating have to invite every girl on the list for spring rush, or can they pick and choose who they invite? If there is anything else you think is important please include it! Also If anyone knows what houses participated in spring rush last year please post them on here! Thanks!