text: CC0 (“CC Zero”) is intended for use only 
  by authors or holders of copyright and 
  
  related rights (including database rights), in connection 
  with works that are still subject to those rights in one or 
  more countries. 
  
  When CC0 is applied to a work, copyright and related 
  rights are relinquished worldwide, making the work free 
  from those restrictions to the greatest extent possible. 
  
  The Public Domain Mark (PDM) is used 
  to label works that are already free of 
  
  known copyright restrictions. Unlike CC0, PDM doesn’t 
  change the copyright status of a work. 
  
  PDM can be used by anyone, and is intended for use 
  with works that are already free of known copyright 
  restrictions throughout the world. 