Comment-based syntax typically uses XML-like comments or special preprocessed comment-like elements to either annotate parts of a Web page (see StructureAnnotation) or to introduce program code into the document (see PythonInWebPage).
See PythonInWebPage for an example using JSP-like syntax. Here is a StructureAnnotation version using HTML-like syntax:
<table>
<!-- loop:item in items -->
<tr>
<th>Name</th>
<td><!-- expr:item.name --></td>
</tr>
<!-- loop:end -->
</table>One potential advantage of comment-based syntax is that HTML-aware tools can ignore the comments, should the syntax have been chosen correctly.