d so it is not required to set it on
  the `paper-ripple` element directly.

Apply `recenteringTouch` class to make the recentering rippling effect.

    <paper-ripple class="recenteringTouch"></paper-ripple>

Apply `circle` class to make the rippling effect within a circle.

    <paper-ripple class="circle"></paper-ripple>

@group Paper Elements
@element paper-ripple
@homepage github.io
-->

<link rel="import" href="../polymer/polymer.html" >

<polymer-element name="paper-ripple" attributes="initialOpacity