Grammar and the Queen's English

Here is something for the grammar-obsessed, and for those who, perhaps, should be grammar-obsessed:

It's is not, it isn't ain't, and it's it's, not its, if you mean it is. If you don't, it's its. Then too, it's hers. It isn't her's. It isn't our's either. It's ours, and likewise yours and theirs.