Merge pull request #16 from PolymerElements/required

form elements can have the required attribute

iron-form-element-behavior.html

@@ -48,6 +48,19 @@
         type: String
       },
 
+      /**
+       * Set to true to mark the input as required. If used in a form, a
+       * custom element that uses this behavior should also use
+       * Polymer.IronValidatableBehavior and define a custom validation method.
+       * Otherwise, a `required` element will always be considered valid.
+       * It's also strongly recomended to provide a visual style for the element
+       * when it's value is invalid.
+       */
+      required: {
+        type: Boolean,
+        value: false
+      },
+
       /**
        * The form that the element is registered to.
        */