title: Understanding why the extends arrow points in the opposite direction
body: <p>In class diagrams I typically see something like ClassA extends ClassB where the arrow head points to ClassA. Example, here, <a href="http://bit.ly/GFakDu" rel="noreferrer">http://bit.ly/GFakDu</a>. This has always confused me. Why is the arrow head not pointing to ClassB? </p>
  
  <p><img src="https://i.stack.imgur.com/fPpIv.jpg" alt="enter image description here"></p>