title: using htmlpurifier for input or output escaping/filtering
body: <p>I am processing a user input from the public with a javascript WYSIWYG editor and I'm planning on using htmlpurifier to cleanse the text.</p>
  
  <p>I thought it would be enough to use htmlpurifier on the input, stored the cleaned input in the database,and then output it without further escaping/filtering.  But I've heard other opinions that you should always escape the output.  </p>
  
  <p>Can someone explain why I should need to clean the output if I'm already cleaning the input?</p>