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="unselectable" >Mens Suggestions</li>
 <li>Jacket</li>
 <li class="unselectable" >Women Suggestions</li>
 <li>Sweater</li> 
</ul>

The short answer is to set the class to ui-autocomplete-category as shown in the example from https://jqueryui.com/autocomplete/#categories

Working example: https://jsfiddle.net/Twisty/183he51q/

HTML

<label for="search">Search: </label>
<input id="search">

CSS

.ui-autocomplete-category {
  font-weight: bold;
  padding: .2em .4em;
  margin: .8em 0 .2em;
  line-height: 1.5;
}

jQuery

$(function() {
  $.widget("custom.catcomplete", $.ui.autocomplete, {
    _create: function() {
      this._super();
      this.widget().menu("option", "items", "> :not(.ui-autocomplete-category)");
    },
    _renderMenu: function(ul, items) {
      var that = this,
        currentCategory = "";
      $.each(items, function(index, item) {
        var li;
        if (item.category != currentCategory) {
          ul.append("<li class='ui-autocomplete-category'>" + item.category + "</li>");
          currentCategory = item.category;
        }
        li = that._renderItemData(ul, item);
        if (item.category) {
          li.attr("aria-label", item.category + " : " + item.label);
        }
      });
    }
  });
  var data = [{
    label: "Jacket",
    category: "Mens Suggestions"
  }, {
    label: "Sweater",
    category: "Mens Suggestions"
  }, {
    label: "Jacket",
    category: "Women Suggestions"
  }, {
    label: "Sweater",
    category: "Women Suggestions"
  }];

  $("#search").catcomplete({
    delay: 0,
    source: data
  });
});