Demo and API docs

##<iron-collapse>

iron-collapse creates a collapsible block of content. By default, the content will be collapsed. Use opened or toggle() to show/hide the content.

<button on-click="toggle">toggle collapse</button>

<iron-collapse id="collapse">
  <div>Content goes here...</div>
</iron-collapse>

...

toggle: function() {
  this.$.collapse.toggle();
}

iron-collapse adjusts the height/width of the collapsible element to show/hide the content. So avoid putting padding/margin/border on the collapsible directly, and instead put a div inside and style that.

<style>
  .collapse-content {
    padding: 15px;
    border: 1px solid #dedede;
  }
</style>

<iron-collapse>
  <div class="collapse-content">
    <div>Content goes here...</div>
  </div>
</iron-collapse>