Блокировка перетаскивания jquery ui sortable

$(function() {
  $("#content").sortable({
    containment: "parent",
    cancel: ".item > input:checked",
  });
});

#content div {
  border: 1px solid;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://code.jquery.com/ui/1.13.0-rc.2/jquery-ui.js" integrity="sha256-bLjSmbMs5XYwqLIj5ppZFblCo0/9jfdiG/WjPhg52/M=" crossorigin="anonymous"></script>
<div id="content">
  <div class="item"><input type="checkbox" checked>1</div>
  <div class="item"><input type="checkbox" checked>2</div>
  <div class="item"><input type="checkbox">3</div>
  <div class="item"><input type="checkbox">4</div>
</div>