GitHub-flavored Markdown with extensions
GitHub-Flavored Markdown (GFM) is the specific dialect of Markdown used across GitHub for documentation, issues, pull requests, and comments. It is a strict superset of CommonMark—the standardized, rigorously defined version of original Markdown.
Because standard Markdown lacks several features heavily needed in software development and collaboration, GFM formalizes these additions as extensions.
The Official GFM Extensions
The features that distinguish GFM from standard CommonMark are formally categorized as extensions within its specification:
- Tables:
Allows you to structure data into rows and columns using pipes (|) and hyphens (-).
- Task Lists:
Enables checklists using bracket syntax (- [ ] for incomplete items and - [x] for completed ones).
- Strikethrough:
Lets you cross out text by wrapping it in double tildes (text).
- Autolinks
- Automatically converts raw URLs and email addresses into clickable hyperlinks without requiring standard Markdown link syntax (text).
- Disallowed Raw HTML (Tagfilter):
- A security extension that blocks or neutralizes potentially dangerous raw HTML tags (such as <script>, <style>, and <iframe>) while still permitting safe formatting tags.
Additional GitHub Markdown Features
Beyond the core GFM specification, GitHub frequently introduces supplemental rendering extensions for documentation:
- Alerts (Callouts):
Special blockquote extensions like > [!NOTE], > [!TIP], or > [!WARNING] that render with distinctive colored banners and icons to emphasize critical information.