How to make jQuery UI autocomplete dropdown ul list item selectively disabled

How to make jQuery UI autocomplete dropdown ul list item selectively disabled

The dropdown  classes  are  ul.ui-autocomplete li.ui-menu-item  by default. I want to make the unselectable  li  not selectable for better UX. i.e. If I enter keywords "coat" in the search bar, it shows Mens Suggestions, then Jacket, then Women Suggestions, then Sweater. When I use arrow keys to select them, it skips the Suggestions part. I have tried  .attr('disabled', ture);, .prop('disabled', true);  and  user-select: none;  none of them is working. It just adds  disabled="disabled"  to the  li , and it is still selectable. Is there a disabled property in jQuery UI I can attach it onto the li to accomplish this?

  <ul class = "ui-autocomplete" >
 <li class="ui-menu-item unselectable" >Mens Suggestions</li> <li>Jacket</li> <li class="unselectable" >Women Suggestions</li> <li>Sweater</li> </ul>