Roll third_party/polymer.

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>
         <div>Item 2</div>
         <div>Item 3</div>
       </iron-selector>
 
   If you want to use the attribute value of an element for `selected` instead of the index,
   set `attrForSelected` to the name of the attribute.  For example, if you want to select item by
   `name`, set `attrForSelected` to `name`.
 
   Example:
 
       <iron-selector attr-for-selected="name" selected="foo">
         <div name="foo">Foo</div>
         <div name="bar">Bar</div>
         <div name="zot">Zot</div>
       </iron-selector>
 
+  If no matching element is found using `attForSelected`, use `fallbackSelection` as fallback.
+
+  Example:
+
+        <iron-selector attr-for-selected="name" selected="non-existing"
+                       fallback-selection="default">
+          <div name="foo">Foo</div>
+          <div name="bar">Bar</div>
+          <div name="default">Default</div>
+        </iron-selector>
+
+  Note: When the selector is multi, the selection will set to `fallbackSelection` iff
+  the number of matching elements is zero.
+
   `iron-selector` is not styled. Use the `iron-selected` CSS class to style the selected element.
 
   Example:
 
       <style>
         .iron-selected {
           background: #eee;
         }
       </style>
 
@@ skipping 10 matching lines @@
 
   Polymer({
 
     is: 'iron-selector',
 
     behaviors: [
       Polymer.IronMultiSelectableBehavior
     ]
 
   });