Optional closing elements in HTML

Several HTML elements do not require closing tagsThere's a dozen or so HTML tags which optional closing tags, so this is legitimate HTML markup

<html>
<head>
<body>
<p>
<dt>
<dd>
<li>
<option>
<th>
<tbody>
<tr>
<td>
<tfoot>
<colgroup>

That means that this is valid html

html

<html>
  <head>
    <title>My blog</title>
    <body>
      <h1>My blog</h1>
      <p>Welcome to my blog</p>
      <p>Here are a list of my posts</p>
      <ul>
        <li>My first post</li>
        <li>My second post</li>
        <li>My third post</li>
      </ul>
    </body>
  </head>
</html>

As a general rule I don't recommend writing html like this, as it can be hard to tell when an element is meant to end or meant to nest, especially when the formatting isn't as clean as possible.