update elements and fix some bugs

lib/src/iron-validatable-behavior/iron-validatable-behavior.html

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 <link rel="import" href="../polymer/polymer.html">
 <link rel="import" href="../iron-meta/iron-meta.html">
 
 <script>
 
   /**
-   * Use `Polymer.IronValidatableBehavior` to implement an element that validates user input.
+   * `Use Polymer.IronValidatableBehavior` to implement an element that validates user input.
+   * Use the related `Polymer.IronValidatorBehavior` to add custom validation logic to an iron-input.
+   *
+   * By default, an `<iron-form>` element validates its fields when the user presses the submit button.
+   * To validate a form imperatively, call the form's `validate()` method, which in turn will
+   * call `validate()` on all its children. By using `Polymer.IronValidatableBehavior`, your
+   * custom element will get a public `validate()`, which
+   * will return the validity of the element, and a corresponding `invalid` attribute,
+   * which can be used for styling.
+   *
+   * To implement the custom validation logic of your element, you must override
+   * the protected `_getValidity()` method of this behaviour, rather than `validate()`.
+   * See [this](https://github.com/PolymerElements/iron-form/blob/master/demo/simple-element.html)
+   * for an example.
    *
    * ### Accessibility
    *
    * Changing the `invalid` property, either manually or by calling `validate()` will update the
    * `aria-invalid` attribute.
    *
    * @demo demo/index.html
    * @polymerBehavior
    */
   Polymer.IronValidatableBehavior = {
@@ skipping 84 matching lines @@
 
     _getValidity: function(value) {
       if (this.hasValidator()) {
         return this._validator.validate(value);
       }
       return true;
     }
   };
 
 </script>