Under the Hood: Property Order, Hidden Classes, Inline Caches and the Cost of delete

Maria asks "but why" more than anyone in the class. In Lesson 01 she saw that a changed key keeps its place, and that keys which look like numbers jump to the front. She wants the rule written down, not a list of surprises. She has also heard that "objects are just hash tables", and that delete is slow. She wants to see both claims tested.