title: Maven <mirror> tag, meaning of external:* parameter
body: <pre><code>&lt;settings&gt;
    ...
    &lt;mirrors&gt;
      &lt;mirror&gt;
        &lt;id&gt;internal-repository&lt;/id&gt;
        &lt;name&gt;Maven Repository Manager running on repo.mycompany.com&lt;/name&gt;
        &lt;url&gt;http://repo.mycompany.com/proxy&lt;/url&gt;
        &lt;mirrorOf&gt;external:*&lt;/mirrorOf&gt;
      &lt;/mirror&gt;
    &lt;/mirrors&gt;
    ...
  &lt;/settings&gt;
  </code></pre>
  
  <p>The official documentation, about the meaning of the <code>external:*</code> parameter within a <code>&lt;mirrorOf&gt;</code> tag, says that:</p>
  
  <blockquote>
    <p>matches all repositories except those using localhost or file based
    repositories. This is used in conjunction with a repository manager
    when you want to exclude redirecting repositories that are defined for
    Integration Testing.</p>
  </blockquote>
  
  <p>Within this context, my question are:</p>
  
  <ul>
  <li>What does it mean that a repository uses localhost?  </li>
  <li>What does it mean that repository is file-based?</li>
  </ul>