There are several test cases rendered in the document.
Each test case represents a different combination of
position and overflow style in a parent and child
containers.
The parent-child pairs are color-coded.
For each test case, a visible sub-rect of a child (the output of
Rect( child ).getVisible() ) is painted as a box with a solid
border and "X" stretching to its boundaries.
For each test case, a total bounding rect of a child is painted as a box with dashed border (could be hidden underneath the visible sub-rect).
Things to verify:
Make sure the latter rect (the one with "X") represents the actual visible subset of a child considering the geometry of the parent. Resize the window to see the visible rect change.
Scroll down to see parent-child paris in the invisible sections of a
viewport. The getVisible() method ignores the rect of the
viewport so the children should be marked as fully visible.