A stacked bar chart visualizes a personal financial plan over time, showing how income, return on capital, and capital itself are spent or retained each year. The chart uses D3 v4 with SVG rendering and animation, computing the plan data via a custom `FinancialPlan` class that simulates yearly cash flows. Bars are grouped by year and colored by category, with mouseover interactions highlighting related spending and retained segments while displaying details in a popup.