Rolling forward https://codereview.chromium.org/1155683008/ which was

third_party/polymer/v1_0/components-chromium/iron-selector/iron-selector-extracted.js

 
   /**
   `iron-selector` is an element which can be used to manage a list of elements
   that can be selected.  Tapping on the item will make the item selected.  The `selected` indicates
   which item is being selected.  The default is to use the index of the item.
 
   Example:
 
       <iron-selector selected="0">
         <div>Item 1</div>
@@ skipping 37 matching lines @@
   Polymer({
 
     is: 'iron-selector',
 
     behaviors: [
       Polymer.IronMultiSelectableBehavior
     ]
 
   });