title: Using coordinatorLayout anchor's with constraintLayout
body: <p>I want to design something like this :</p>
  
  <p><a href="https://i.stack.imgur.com/orN4Z.png" rel="noreferrer"><img src="https://i.stack.imgur.com/orN4Z.png" alt="enter image description here"></a></p>
  
  <p>as you can see fab is between header and the body.</p>
  
  <p>it's easy to do it with <strong>coordinatorLayout</strong> with <code>app:anchor</code> and <code>app:anchorGravity</code> attributes</p>
  
  <p>but i want to do it with <strong>constraintLayout</strong>.</p>
  
  <p>any ideas ?</p>