[Quoth]

Self closing tags are also alternatively known as void tags, empty tags, singletons tags, etc. i.e these tags do not have contents and also can not have any child.
Container tags can be empty <tag></tag>

The Void / Empty / Singleton / Inherently self closing tags may end in />, but some do not.
They can't be written as an opening and closing tag. Illegal (malformed) XML/HTML
<hr></hr>
<br></br>
<col></col>

So container tags can be <tag></tag>, i.e. have no content.
But singleton tags are never a pair of opening and closing tags, they are self closing, complete, though some end in /> and some contexts will accept <br> and <hr>.

The comment is a special case of void or singleton
<!-- This is a comment -->

But this also is a valid comment tag. All the enclosed HTML is disabled.

<!-- 
<ul class="top_menu_right">
			<li>
				<form action="search.php" method="post">
				<input type="hidden" name="do" value="process" />
				<input type="hidden" name="showposts" value="0" />
				<input type="hidden" name="childforums" value="1" />
				<input type="hidden" name="securitytoken" value="1723152374-234a53b9ef86581494348ed4767ee7d9f993eecf" />
				<input type="hidden" name="s" value="" />
				<input type="text" class="button" name="query" size="20" style="width:120px" />
				<input name="search" value="Search" type="submit" class="button" style="width: 5em;" />
				</form>
			</li>
			</ul>
-->

An ebook can have comments, but unlike web pages, shouldn't need them.