markdown-it.md

diagnostics	line column message 3 1 unsupported TOC directive `[[toc]]`; mdsmith has no heading TOC equivalent; use `<?catalog?>` for file indexes (MDS019)

markdown-it / VitePress TOC directive

[[toc]]

markdown-it-toc-done-right and VitePress replace this with a generated heading TOC; CommonMark leaves it as literal text.