Re: [gcpm][books] thematic breaks at the top of a page

Tab Atkins Jr. wrote:
> As usual for proposals for style/layout-based selectors, this has the
> potential for circular dependencies.  What happens if you use the
> selector to move the element away from the top of the page, such that
> something else is now at the top?  For example, you might float it, or
> use the 'order' property, etc.

That is true.  At least for this simple example, we could handle it by 
just changing say the visibility of the element.  We could restrict the 
properties allowed within :at-top-of-page (or whatever) like we do for 
::before.