keeping this straight forward for the new element's initial inclusion.being that this is a new element, the reasoning for authors to need to immediately apply overwriting roles is irrelevant.  Thus I see no reason to initially allow any roles on this element.All global `aria-*` attributes would be allowed on this element.

the additional roles added to the search element allowances are to provide reasonable roles that developers may need to use while the search element is still being implemented by browsers, as well as roles which might be reasonable 'fixes' for someone who used the element per their understanding of its semantics, but was not aware of the landmark region it creates, which is not appropriate in context of their web page.