title: jsdoc two dimensional array
body: <p>I have an array of array of string and I can't figure out how to document that with JSDoc.</p>
  
  <pre><code>/**
  @class
  */
  function PostbackList() {
      /**
      @type {int}
      @default
      */
      this.TypeID = 0;
      /**
      @type {PostbackList.Field[]}
      */
      this.Fields = new Array();
      /**
  
      !! Issue here !!
  
  
      @type {string[][]}
      */
      this.Values = null;
  }
  </code></pre>
  
  <p>Which results in errors.</p>
  
  <blockquote>
    <p>Invalid type expression "string[][]": Expected "!", "?" or "|" but "["
    found.</p>
  </blockquote>
  
  <p>And I don't know if I should put <code>?</code> in front of the type to indicate it can be null.</p>