Markdown doesn't have a comment.  There are eleventy bazillion different ways of simulating a comment by abusing things to effectively hide a chunk of text, but they are all very sensitive to which Markdown renderer you are using.  The safest bet is a `<div>` with a style that sets `display` to `none`.  The <<linkFromPath path:"$:/ou/styles/Hidden" hidden>> class does this:

```
<div class="hidden">
some text that you don't want to appear in the document
</div>
```

The text is still in the HTML, so don't use this to hide anything sensitive.