From the article:

Flint is a visualization intermediate language that lets AI agents reliably create expressive, good-looking charts from simple, human-editable chart specs. Instead of requiring verbose low-level parameters such as scales, axes, spacing, and layout, the Flint compiler derives optimized chart settings from the data, semantic types, chart type, and encodings. Flint supports 46 chart types, and it supports rendering in Vega-Lite, ECharts, and Chart.js.