title: Angular Drag & Drop: cdkDrag item dropping in nested cdkDropLists
body: <p>Stackblitz to showcase issue: <a href="https://stackblitz.com/edit/angular-ivy-tzyvbe?file=src%2Fapp%2Fapp.component.html" rel="nofollow noreferrer">https://stackblitz.com/edit/angular-ivy-tzyvbe?file=src%2Fapp%2Fapp.component.html</a></p>
  <p>I have a outer cdkDropListGroup, and inside two cdkDropLists.</p>
  <p>The first cdkDropList also has two drop lists in it.</p>
  <p>I want to be able to drop a cdkDrag item into the first cdkDropList but also into the nested cdkDropLists inside it if dropping into them.</p>
  <p>You can see I'm logging the dropList you drop the item into and it is always the outer droplist id.</p>
  <p>How can I drop inside nested droplists or is this even possible?</p>