nested test
This example shows a small table and an SVG text hierarchy built from a CSV file. The table renders a 4x4 matrix, transforming each cell value by adding its row index multiplied by two. The SVG displays nested text elements, first grouping months by the `cat` column using `d3.nest`, then attempting to append a second level of text based on the group index. The code uses `d3.select`, `d3.csv`, `d3.nest`, and SVG `text` elements, with data loaded from `data.csv`.