

<link rel="import" href="boot.html">
<link rel="import" href="../mixins/property-effects.html">
<link rel="import" href="../mixins/mutable-data.html">

<script>
  (function() {
    'use strict';

    // Base class for HTMLTemplateElement extension that has property effects
    // machinery for propagating host properties to children. This is an ES5
    // class only because Babel (incorrectly) requires super() in the class
    // constructor even though no `this` is used and it returns an instance.
    le