bi-09 step 01 — Display list and paint order

Goal

mini-browser M10: produce a recording rather than pixels, and demonstrate that paint order is not DOM order.

Tasks

1. Walk your layout tree in paint order and emit display items ({type, rect, color, …}). Do not draw yet — the separation is the point.
2. Implement z-index and stacking contexts. Build a test case whose rendering changes when you remove the stacking-context rule.
3. Implement at least one property that creates a stacking context for purely visual reasons (opacity < 1). Demonstrate that adding it changes structure, not just appearance.
4. Write out the list of stacking-context triggers you support, and name three more from the spec you did not implement.

Done when

• A display list exists, distinct from any raster step
• A z-index case that breaks without stacking contexts
• You can explain why opacity: 0.99 "fixes" z-index bugs — and why it is a smell