title: Check if custom element prototype is derived from a specific prototype
body: <p>I'm creating a custom element as follows:</p>
  
  <pre><code>var myElementProto = Object.create(HTMLElement.prototype);
  document.registerElement('my-element', myElementProto);
  </code></pre>
  
  <p>Based on this element, I'll be creating some other elements which will inherit all of the methods and attributes I've defined on this element, like so:</p>
  
  <pre><code>var myNewElementProto = Object.create(myElementProto);
  document.registerElement('my-newElement', myNewElementProto);
  </code></pre>
  
  <p>What I'd like to do is have some standard ways in which these elements interact with each other in the DOM, but I'm not sure what the best way of identifying all of the other defined elements are. Is there a way for me to check if a given element has a prototype that's a descendant of <code>myElementProto</code> without just checking to see if it has certain properties I'm defining on <code>myElementProto</code>? That approach seems like it would work, but might cause problems down the line if those properties end up getting changed/removed, so I'd rather avoid it.</p>