Markdown is a lightweight markup language created by John Gruber in 2004, later formalized as CommonMark. The rendering pipeline consists of two stages: parsing and HTML generation. The parser tokenizes the Markdown source into an AST of block-level elements (headings, paragraphs, lists, blockquotes, code blocks) and inline elements (bold, italic, links, images, code spans).

Block parsing is line-oriented: the parser examines each line to determine if it starts a new block (e.g., # for headings, - for list items, > for blockquotes) or continues an existing one. Inline parsing then processes the text content within each block, handling nested emphasis (** for bold, * for italic), link references, and escape sequences. The resulting AST is walked to produce sanitized HTML output. GFM extensions add table parsing (pipe-delimited columns with alignment markers), task list detection (- [ ] and - [x]), autolinked URLs, and strikethrough (~~ delimiters). The preview updates on every keystroke using a debounced render cycle for smooth performance.