The test shows 3 grids each of them with 3 items sorted differently in the DOM.
Each grid container must use its first (grid order) item to compute its baseline, and using document-oder in case of element with same grid-order. Hence they might be baseline aligned each other accordingly.

This case shows 3 items located along the first row and in different columns. The grid baseline is computed using the one located at first column (blue item) regardless of source order.

This case shows 3 items located along the first row and in different columns. The baseline-aligned item (blue) always determines the grid baseline.

This case shows 3 items' areas intersecting the first row and first column, but none of them participate in baseline alignment in the first row, so the dom order must be used to determine each grid's baseline.

This case shows 3 items' areas intersecting the first row and first column, but one of the items participates in baseline alignment in the first row, so such item is used to determine the grid's baseline instead of using the dom order.

This case shows one of the grids with no items, hence its baseline must be synthesized from its margin box.

This case shows two of the grids with no items in their first row, hence the items in the second row are evaluated.