Determine which type of data is being drag over in HTML

I have two lists, each with different kind of data. I'm trying to implement some way to let the user reorder the list items inside of them, but I don't want them to mix things up. I'm using HTML's ondrop, ondragover and ondragstart, but I can't seem to figure how to get any data in the ondragover event in order to either allow or disallow the drop. I've already set data in ondragstart and I can get it in ondrop events, but it seems like I'm unable to get it inside ondragover.