From W3C Wiki
The <hgroup> element was introduced in HTML 5 and was used to group a set of h1–h6 elements when the heading has multiple levels.
It is now deprecated.
See global attributes.
Don't use this anymore:
<hgroup> <h1>The reality dysfunction</h1> <h2>Space is not the only void</h2> </hgroup>
Use that instead:
<header> <h1>The reality dysfunction</h1> <p class="subheading">Space is not the only void</p> </header>