title: ValueError: Invalid PI name 'xml' when running spcchart
body: <p>I'm trying to run spcchart on Python 2.7 environment and turn out an error "ValueError: Invalid PI name 'xml'".
  Error message attached and if anyone can tell where went wrong and how to fix it, thank you!</p>
  
  <p><img src="https://i.stack.imgur.com/xqXEt.jpg" alt="enter image description here"></p>