chrome/common/extensions/docs/templates/intros/extension.html

<h2 id="content scripts">Support for content scripts</h2>
<p>
Unlike the other chrome.* APIs,
parts of <code>chrome.extension</code>
can be used by content scripts:
</p>

<dl>
  <dt>
    $ref:runtime.sendMessage and
    $ref:runtime.onMessage
  </dt>
  <dd>
    Simple communication with extension pages
  </dd>
  <dt>
    $ref:runtime.connect and
    $ref:runtime.onConnect
  </dt>
  <dd>
    Extended communication with extension pages
  </dd>
  <dt>
    $ref:extension.getURL
  </dt>
  <dd>
    Access to extension resources such as image files
  </dd>
</dl>

<p>
For details, see
<a href="content_scripts.html">Content Scripts</a>.
</p>