title: Chrome Extension : Modify DOM before loading
body: <p>My Chrome Extension should modify a DOM element before the DOM is fully constructed, and in the best scenario, right after this DOM element is constructed.</p>
  
  <p>For example, if I have a  in my document, I want to wait until it is constructed, then directly modify it, before the rest of the DOM is constructed.</p>
  
  <p>But I only managed to access the DOM before the  element is constructed and after the entire DOM is constructed.</p>
  
  <p>So how do I listen to the construction of a special element ?</p>