I have discovered what appears to be a useful feature of searching family events such as marriage and divorce. I considered posting this message in Tips, but I thought that I would first confirm that my observations are correct.
Suppose we have person A who has children with each of person X, person Y, and person Z. Suppose I have a marriage record for person A married to person X and a marriage record for person A married to person Z, but I don't have a marriage record for person A married to person Y. That doesn't necessarily mean that person A and person Y were never married nor that their children together were born out of wedlock. It may simply mean that I haven't yet found the marriage record for person A and person Y.
In any case, if I set up a search for Number of spouses -> not equal to -> 0 AND Marriage -> exists -> is False, then who is found by the search? Well, the search certainly finds person Y and the search certainly does not find person X or person Z. These results are expected. But the search does also find person A. This is a little unexpected, but nevertheless it can be a very useful result. The result is unexpected because person A manifestly does have a marriage fact - indeed person A has two marriage facts. But the result is also very useful because person A does not have a marriage fact for person Y. Hence, I was thinking of making this into a Tip, assuming my understanding of the search results is correct.