code: @SuppressWarnings("unchecked")
      public <T extends XPathBuilder> T setClasses(final String... classes) {
          if (classes != null) {
              this.classes = Arrays.asList(classes);
          }
          return (T) this;
      }
docs: <p><b>Used for finding element process (to generate xpath address)</b></p>
  <p>Use it when element must have all specified css classes (order is not important).</p>
  <p>Example:</p>
  <pre>
  WebLocator element = new WebLocator().setClasses("bg-btn", "new-btn");
  </pre>
  <ul>
  <li>Provided classes must be conform css rules.</li>
  </ul>
  
  @param classes list of classes
  @param <T>     the element which calls this method
  @return this element