foo should not contain HTML unless declared in the type attribute

This element contains escaped HTML, but it has declared itself as "text".

Use the type attribute to declare that this is HTML. For example, this is an invalid title in an Atom feed:

<title>My &lt;b&gt;Bold&lt;/b&gt; Title</title>

To make it valid, add the following attribute:

<title type="html">My &lt;b&gt;Bold&lt;/b&gt; Title</title>