Default

<aside>
  <h2>This is a heading 2</h2>
</aside>

aside with aria-labelledby

<aside aria-labelledby="aside_heading">
  <h2 id="aside_heading">This is a heading 2</h2>
</aside>

aside with aria-label

<aside aria-label="This is a heading 2">
  <h2>This is a heading 2</h2>
</aside>