There are rules to writing that we all try to follow so that we communicate clearly and so that we don’t look like idiots to our readers. These are not editors’ rules; they are language rules. And there’s one that’s just been broken on Yahoo! Style:
The plural of parent is parents; the possessive of parents is parents’. I think that means that parents’s is the singular possessive of the plural parents. Or maybe it just means the writer has no idea what she’s doing.