title: Typechecking nested object properties with PropType
body: <p>I have following that i want to annotate with flow:</p>
  
  <pre><code>type PropType = {
    content: Object
  };
  
  export const DialogContent = ({ content }: PropType) =&gt; (
    &lt;div&gt;
      &lt;p className={cn('text-head')}&gt;{content.h4}&lt;/p&gt;
      &lt;p className={cn('text-bottom')}&gt;
        {content.p}
      &lt;/p&gt;
    &lt;/div&gt;
  );
  </code></pre>
  
  <p>I know how to do the type-check to so that <code>content</code> is of type <code>Object</code> (as shown above), but how can I type-check its properties as well?</p>
  
  <hr>
  
  <p>Already tried this:</p>
  
  <pre><code>  type PropType = {
    content: {
      p: string,
      h4: string
    }
  };
  </code></pre>
  
  <p>But then flow just complains that <code>p</code> and <code>h4</code> is never used.</p>