Markdown comments
Markdown has no comment syntax. An HTML comment is the usual way to leave a note in the file that does not appear in the rendered page.
<!-- This note is not rendered. --><!--
A longer note.
Still hidden.
-->[comment]: # (This is not rendered either.)An abused link definition. It never matches a link, so nothing shows.
What usually goes wrong
- Hidden is not private. The comment sits in the file in plain text, and anyone who opens the source or views the page source can read it.
- A comment inside a fenced code block is not a comment. It is code, and it renders.
- Some strict renderers escape HTML comments and print them. The link-definition trick survives those.