title: what is the usage of a marker interface that inherit from another interface?
body: <p>for example:</p>
  <pre><code>public interface ITagHelper : ITagHelperComponent
  {
  }
  </code></pre>
  <p>I understand <code>ITagHelper</code> is used as a marker interface which doesn't contain any member, but since it inherits from <code>ITagHelperComponent</code>, then why not just use <code>ITagHelperComponent</code> as a marker interface directly? what's the point to have one extra layer of abstraction?</p>