Abstract Syntax Trees

https://www.ryanfiller.com/blog/remark-and-rehype-plugins

To paraphrase heavily from the mdsvex docs, the source file is first parsed into a Markdown AST (MDAST), where remark plugins run. Then the data is converted into an HTML AST (HAST), where rehype plugins run. Finally the data is converted (stringified) into valid markup for the browser.