Upgrade to 1.0 and switch clients to dom-repeat where needed.

third_party/polymer/v0_8/components/paper-input/paper-input-error.html

 <!--
 @license
 Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 Code distributed by Google as part of the polymer project is also
 subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 -->
 
 <link rel="import" href="../polymer/polymer.html">
 <link rel="import" href="../paper-styles/paper-styles.html">
+<link rel="import" href="paper-input-addon-behavior.html">
 
 <!--
-`<paper-input-error>` is an error message for use with `<paper-input-container>`.
+`<paper-input-error>` is an error message for use with `<paper-input-container>`. The error is
+displayed when the `<paper-input-container>` is `invalid`.
+
+    <paper-input-container>
+      <input is="iron-input" pattern="[0-9]*">
+      <paper-input-error>Only numbers are allowed!</paper-input-error>
+    </paper-input-container>
+
+### Styling
+
+The following custom properties and mixins are available for styling:
+
+Custom property | Description | Default
+----------------|-------------|----------
+`--paper-input-container-invalid-color` | The foreground color of the error | `--google-red-500`
+`--paper-input-error`                   | Mixin applied to the error        | `{}`
 -->
 <dom-module id="paper-input-error">
 
   <style>
 
     :host {
       /* need to use display: none for role="alert" */
       display: none;
       float: left;
 
-      color: var(--paper-input-container-invalid-color);
+      color: var(--paper-input-container-invalid-color, --google-red-500);
 
-      mixin(--paper-input-container-add-on);
-      mixin(--paper-input-container-add-on-font);
-
-      mixin(--paper-input-error);
+      @apply(--paper-font-caption);
+      @apply(--paper-input-error);
     }
 
     :host([invalid]) {
       display: inline-block;
     };
 
   </style>
 
   <template>
 
     <content></content>
 
   </template>
 
 </dom-module>
 
 <script>
 
 (function() {
 
   Polymer({
 
     is: 'paper-input-error',
 
-    enableCustomStyleProperties: true,
+    behaviors: [
+      Polymer.PaperInputAddonBehavior
+    ],
 
     hostAttributes: {
-      'add-on': '',
       'role': 'alert'
     },
 
     properties: {
 
       /**
-       * Set to true to show the error.
+       * True if the error is showing.
        */
       invalid: {
+        readOnly: true,
         reflectToAttribute: true,
         type: Boolean
       }
 
     },
 
-    attached: function() {
-      this.fire('addon-attached');
+    update: function(state) {
+      this._setInvalid(state.invalid);
     }
 
   })
 
 })();
 
 </script>