title: Extending a typescript variable declaration
body: <p>I want to use the <a href="https://github.com/tellnes/nconf-yaml" rel="nofollow noreferrer">nconf-yaml</a> plugin with my Typescript project, but I don't know how to add it in my typings. In <em>@types/nconf</em>, the <code>formats</code> variable is declared as below:</p>
  
  <pre><code>export declare var formats: {
      json: IFormat;
      ini: IFormat;
  };
  </code></pre>
  
  <p>How do I use declaration merging to add yaml, so that it will become:</p>
  
  <pre><code>export declare var formats: {
      json: IFormat;
      ini: IFormat;
      yaml: IFormat
  };
  </code></pre>