To surround the comments document that will be ignored by HTML parser. Text in tag <!-- --> is not shown in the browser window.
<!-- -->
<HTML>
<Head>
<Title>...</Title>
<!-- This document is edited by Sothink -->
</Head>
...
</HTML>
Comments can contain other HTML elements. Comments can not nested. White space is allowed between the closing -- and >, but not between the opening.
Both the start and end tags are required.