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CommonMark is a standardised specification that resolves ambiguities in the original Markdown. GitHub Flavored Markdown (GFM) is a superset of CommonMark that adds tables, strikethrough (~~text~~), task lists (- [x]), and fenced code blocks with language identifiers. GFM is the format used in GitHub READMEs, issues and pull request descriptions.

MDX is Markdown extended with JSX — it lets you use React components inside Markdown files. Popular in documentation sites built with Gatsby, Next.js or Astro, where you want the simplicity of Markdown for text but the power of React for interactive elements like demos and callout components.

Email clients do not natively render Markdown. Some tools (HEY, Notion) convert Markdown to HTML before sending. For standard emails, export your Markdown as HTML first, then use that HTML in your email campaign tool. Email HTML has strict CSS support limitations to be aware of.

Use pipes for columns and hyphens for the header separator: | Header 1 | Header 2 | on one line, then | --- | --- |, then data rows. Alignment: |:---| for left, |:---:| for center, |---:| for right. Tables are a GFM extension — not all parsers support them.