footer.html

<element name='footer'>

  <template>
    <div id='{{id}}' style='{{style}}' persist='{{persist}}' data-fullscreen='{{data-fullscreen}}' data-position='{{data-position}}' data-theme='{{data-theme}}' data-role='footer'>
      <content></content>
    </div>
  </template>

  <script>
  registerElement('footer', {

    init: function() {
      if (typeof this.$ele.attr('persist') === 'undefined') {
        this.$ele.attr('data-id', 'persist');
      }
    }

  });
  </script>

</element>