<hn> Heading Tags in HTML 5

The <h1> through <h6> tags are the most frequently used heading tags in HTML. When heading tags are not grouped inside a hgroup element, the heading level is simply the number in the element name of the heading tag. When they are inside a heading group, the level represented by the whole group is the lowest number of the enclosed heading tags.

LevelUngroupedGrouped LevelUngroupedGrouped
Level 1
<h1>...</h1>
<hgroup>
   <h1>...</h1>
   <h2>...</h2>
   ...
</hgroup>
 Level 4
<h4>...</h4>
<hgroup>
   <h4>...</h4>
   <h5>...</h5>
   ...
</hgroup>
Level 2
<h2>...</h2>
<hgroup>
   <h2>...</h2>
   <h3>...</h3>
   ...
</hgroup>
 Level 5
<h5>...</h5>
<hgroup>
   <h5>...</h5>
   <h6>...</h6>
   ...
</hgroup>
Level 3
<h3>...</h3>
<hgroup>
   <h3>...</h3>
   <h4>...</h4>
   ...
</hgroup>
 Level 6
<h6>...</h6>
<hgroup>
   <h6>...</h6>
   <h6>...</h6>
   ...
</hgroup>