title: In typescript, what is the index signature identifier for?
body: <p>What does the index signature identifier do?</p>
  
  <pre><code>interface IIndex {
    [something: string]: any;
  }
  </code></pre>
  
  <p>Where would anyone use "something" again?</p>
  
  <p>Or in other words, why isn't the syntax just:</p>
  
  <pre><code>interface IIndex {
    [string]: any;
  }
  </code></pre>