HTML integration

[marcoscaceres]

Notes on where this specification needs better integration with HTML:

• [ ] In the set the active document algorithm, the relevant's Screen's type and angle should be set. That would solve browsing context initialization (create a new browsing context) at the right point in time.
• [x] The "page visibility change steps" should be moved the HTML.
• [ ] creating the browsing context must set the type and angle attributes