<human>: Can you give me the gist of the text in a nutshell?

This is a general question that has nothing to do with me personally, but I live in MA in case that matters to you :). I read a comment on another website that made me realize I'm not sure I fully understand what a prenup is. My belief was that it says "what's mine is mine, what's yours is yours!" if a couple gets a divorce. I believed this meant each person leaves with his/her own income. However, a comment I read on a news site made me wonder if I misunderstood. It seems in this person's case, the prenup was simply an agreement about how to divide things in case of a divorce (which seems totally reasonable!!). The commenter seems to have not divided things exactly evenly, but he and his wife seem to have agreed to that and were just fine with it when they did get divorced because it was what they agreed to. Do couples sometimes have other arrangements such as allowing some spousal support for some amount of time if one person makes more money than the other (that was what threw me off in the reader's comment)? What varieties of prenups have you seen? P.S. if there is a more fitting sub where I should post this question just let me know!
<bot>: Do couples decide how to divide things in a prenup or does it always mean you just leave with your own income? Can you explain the range/variety of arrangements you have seen in prenups?