title: Can two UML sequence diagram frames overlap?
body: <p>is it acceptable to overlap two frames in a uml sequence daigram? </p>
  
  <p>For example two opt frames:</p>
  
  <p><a href="https://i.stack.imgur.com/bXmYC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bXmYC.png" alt="enter image description here"></a></p>