Gittin 82: Exceptions That Seem to Break the Rules

Chapter 9! A new mishnah - a divorce with the vocabulary of "ehla" - permitted to any man, but rather except... But doesn't that language stipulate a condition, in which case, how do they proceed? Is it a get on condition that she can't marry someone specific? Or does it specify whom she can marry?? A parallel case of "negaim" - house tzara'at - can help explain this "ehla." Also, betrothal with the exclusion of everyone except for one, and that one does the same betrothal. But how strange - to be betrothed to two people!