title: How to obtain the stacking order of all elements in a webpage?
body: <p>That is, how can I obtain a complete, total ordering of all the elements according to their rendered, stacking order programmatically? I need this to determine whether any element is above/below the other element.</p>
  
  <p>Note that merely checking if two elements geometrically overlap is not good enough. I truly need the stacking order (i.e. who is located above/below whom).</p>