title: How to extend JQuery 3 selector in TypeScript
body: <p>After upgrading JQuery from 2 to 3, the latest TypeScript definition no longer contains:</p>
  
  <pre><code>expr: any;
  </code></pre>
  
  <p>Our code base extends the JQuery selector to provide a case insensitive selector:</p>
  
  <pre><code>    $.extend($.expr[":"], {
          containsCaseInsensitive: (elem: any, i: number, match: any, array: any) =&gt;
              (elem.textContent || elem.innerText || "").toLowerCase().indexOf((match[3] || "").toLowerCase()) &gt;= 0
      });
  </code></pre>
  
  <p>With the latest TS definition, this no longer transpiles.  Is there a way to provide the same functionality in JQuery 3 without manually updating the TS definition for JQuery?</p>