title: How to create a custom ul element with polymer dart which fires on-added and on-remove event when children are added?
body: <p>I have been making a simple todo list as a way to learn polymer dart.
  <a href="https://stackoverflow.com/questions/26639961/why-does-hosthover-not-work-here%22todo%20example%22">Here is my todo example</a>.
  I have limited experience in web-programming in general. My idea is to create a simple app with </p>
  
  <ul>
  <li>One text input </li>
  <li>2 Custom ul elements (New task ul and Done task ul)</li>
  <li>Entering a string in text input and pressing enter creates a li item which is added to New task.</li>
  <li>Deleting an element from New task results in addition of element to Done task.</li>
  <li>Now I know creating a separate model and tracking the changes in an observable list seperate from html might be better approach. But as a learning exercise I would like to create a custom ul which fires a on-added and on-removed event when li item are added and removed from it respectively.</li>
  </ul>
  
  <p>Now I have a couple of questions.</p>
  
  <ol>
  <li><p>Why is there no on-added or on-remove event in ul (html)? I would like to understand what is the rational behind it.</p></li>
  <li><p>How would one go about creating a custom UListElement which fires on-added and on-removed event when li items are added or removed from it respectively?</p></li>
  </ol>