Re: Please add the need of position relative in first exampl
I understand what you're saying, but saying that would not be quite accurate. It doesn't actually require position:relative in all cases -- sometimes it's not required and can have undesired consequences, sometimes it's better to give the parent element position:relative and a z-index -- so doing what you suggest would be a bit misleading.
I do however realize that users need more guidance up front to make them aware of the z-index issue. I'm open to making the existing link to the known issues page more obvious, or some other way to make sure users get that information.