In HTML5, there are iframe, which can contain an HTML document inside the parent document. There are several sanboxing options as this W3C page shows it. As far as I understand it, it prevents the iframe scripts from accessing/modifying/interfering with the parent DOM. That is a parent protection against its child.
Now, in HTML5, is there a parameter of the iframe (or it could be another tag) that prevent the parent page to access to the iframe content? Meaning, a child protection against its parent? And of course, if it is an iframe attribute, that would need to be an attribute that can't be removed through a javascript call such as ".removeAttribute()".