This example is a brushable scatter plot matrix of the Iris dataset, showing pairwise relationships between sepal and petal measurements with points colored by species. The matrix features histograms along the diagonal and scatter plots in off-diagonal cells, where users can brush to highlight selections across all panels. Built with D3 v4 and SVG, it uses `d3.brush()` for interactive brushing, `d3.scaleLinear` and `d3.scalePoint` for positioning, and `d3.histogram()` to bin data for the diagonal distributions. The visualization is derived from the classic brushable scatter plot matrix example, adapted to include per-cell axes and histograms.