This example visualizes the frequency of student grades (from "sehr gut" to "ausreichend") split by degree type (master or bachelor) as a stacked bar chart. The data is aggregated using `d3.nest()` and `rollup` to count occurrences per category, then transformed into a stacked layout with `d3.stack()`. The chart uses D3 v5’s `scaleBand` for the x-axis and `scaleLinear` for the y-axis, rendering bars as SVG groups. The code is based on a bar chart from a jsFiddle and a toolkit from bl.ocks.org, with styling defined in an external stylesheet.