gistfile1.html

/*** Declaritive Definition ***/

<element tagname="x-foo">
  <prototype>
    this.bar = function(){ ... }
    this.registeredCallback = function(){
      document.addEventListener('click', function(event){
        if (event.target.nodeName == 'X-FOO'){
          // Do something when any <x-foo> is clicked
        }
      })
    }
  </prototype>
</element>

/*** HTML Usage ***/

<x-foo>BAR!</x-foo>