hgroup elementh1, h2, h3, h4, h5, and/or h6 elements.HTMLElement.The hgroup element represents the
  heading of a section. The element is used to group a set of
  h1–h6 elements when the heading has
  multiple levels, such as subheadings, alternative titles, or
  taglines.
Other elements of heading content in the
  hgroup element indicate subheadings or subtitles.
The rank of an hgroup element is the
  rank of the highest-ranked h1–h6
  element descendant of the hgroup element, if there are
  any such elements, or otherwise the same as for an h1
  element (the highest rank).
The section on headings and sections
  defines how hgroup elements are assigned to individual
  sections.
Here are some examples of valid headings.
<hgroup> <h1>The reality dysfunction</h1> <h2>Space is not the only void</h2> </hgroup>
<hgroup> <h1>Dr. Strangelove</h1> <h2>Or: How I Learned to Stop Worrying and Love the Bomb</h2> </hgroup>
The point of using hgroup in these examples is to
   mask the h2 element (which acts as a secondary title)
   from the outline algorithm.
How a user agent exposes such multi-level headings in user interfaces (e.g. in tables of contents or search results) is left open to implementors, as it is a user interface issue. The first example above could be rendered as:
The reality dysfunction: Space is not the only void
Alternatively, it could look like this:
The reality dysfunction (Space is not the only void)
In interfaces where a title can be rendered on multiple lines, it could be rendered as follows, maybe with the first line in a bigger font size:
The reality dysfunction Space is not the only void