When structs nest, chain dot operators to reach inner members. Each dot goes one level deeper. Read left to right: each step takes you further into the structure. Example: rect.topLeft.x = 10; means "from rect, go to topLeft, from there go to x, then assign 10." You drill through layers.
Three levels means three dots. Think of folders on a computer. rect is the folder, topLeft is a subfolder, x is a file. Use with dots instead of slashes.