The Mobile Viewports

What are the three viewports? (Spoiler: layout, visual, and ideal.) Why do we need all three? Why does responsive design work? (Not how. Why.) What happens when you set the meta viewport? How do browsers go wrong? (Spoiler: in plenty of innovative ways.) And what about resolution, or DPR? (Spoiler: it is not what you think it is.) In this session PPK, who spent more time on the mobile viewport than anyone not working for a browser vendor, answers these questions and more.