Custom Syntax's are now enabled via template.bindingDelegate =

sdk/lib/html/dart2js/html_dart2js.dart

 /// The Dart HTML library.
 ///
 /// For examples, see
 /// [Dart HTML5 Samples](https://github.com/dart-lang/dart-html5-samples)
 /// on Github.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide Symbol, deprecated;
@@ skipping 8596 matching lines @@
    * Gets the content of this template.
    * This is only supported if [isTemplate] is true.
    */
   @Experimental()
   DocumentFragment get content {
     _ensureTemplate();
     return _templateContent;
   }
 
   /**
-   * Creates an instance of the template.
+   * Creates an instance of the template, using the provided model and binding
+   * delegate.
+   *
    * This is only supported if [isTemplate] is true.
    */
   @Experimental()
-  DocumentFragment createInstance(model, String syntax) {
+  DocumentFragment createInstance(model, BindingDelegate delegate) {
     _ensureTemplate();
-    return TemplateElement.mdvPackage(this).createInstance(model, syntax);
+    return TemplateElement.mdvPackage(this).createInstance(model, delegate);
   }
 
   /**
    * The data model which is inherited through the tree.
    * This is only supported if [isTemplate] is true.
    */
   @Experimental()
   get model => TemplateElement.mdvPackage(this).model;
 
   @Experimental()
   void set model(value) {
     _ensureTemplate();
     TemplateElement.mdvPackage(this).model = value;
   }
 
+  /**
+   * The binding delegate which is inherited through the tree. It can be used
+   * to configure custom syntax for `{{bindings}}` inside this template.
+   *
+   * This is only supported if [isTemplate] is true.
+   */
+  @Experimental()
+  BindingDelegate get bindingDelegate =>
+      TemplateElement.mdvPackage(this).bindingDelegate;
+
+  @Experimental()
+  void set bindingDelegate(BindingDelegate value) {
+    _ensureTemplate();
+    TemplateElement.mdvPackage(this).bindingDelegate = value;
+  }
+
   // TODO(jmesserly): const set would be better
   static const _TABLE_TAGS = const {
     'caption': null,
     'col': null,
     'colgroup': null,
     'tbody': null,
     'td': null,
     'tfoot': null,
     'th': null,
     'thead': null,
@@ skipping 12737 matching lines @@
   @DocsEditable()
   Element $dom_insertRow(int index) native;
 }
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // WARNING: Do not edit - generated code.
 
 
-
 /**
  * Model-Driven Views (MDV)'s native features enables a wide-range of use cases,
  * but (by design) don't attempt to implement a wide array of specialized
  * behaviors.
  *
  * Enabling these features in MDV is a matter of implementing and registering an
  * MDV Custom Syntax. A Custom Syntax is an object which contains one or more
  * delegation functions which implement specialized behavior. This object is
- * registered with MDV via [TemplateElement.syntax]:
+ * registered with MDV via [Element.bindingDelegate]:
  *
  *
  * HTML:
- *     <template bind syntax="MySyntax">
+ *     <template bind>
  *       {{ What!Ever('crazy')->thing^^^I+Want(data) }}
  *     </template>
  *
  * Dart:
- *     class MySyntax extends CustomBindingSyntax {
+ *     class MySyntax extends BindingDelegate {
  *       getBinding(model, path, name, node) {
  *         // The magic happens here!
  *       }
  *     }
- *
  *     ...
- *
- *     TemplateElement.syntax['MySyntax'] = new MySyntax();
+ *     query('template').bindingDelegate = new MySyntax();
+ *     query('template').model = new MyModel();
  *
  * See <https://github.com/polymer-project/mdv/blob/master/docs/syntax.md> for
  * more information about Custom Syntax.
  */
-// TODO(jmesserly): if this is just one method, a function type would make it
-// more Dart-friendly.
-@Experimental()
-abstract class CustomBindingSyntax {
+// TODO(jmesserly): move this type to the MDV package? Two issues: we'd lose
+// type annotation on [Element.bindingDelegate], and "mdv" is normally imported
+// with a prefix.
+abstract class BindingDelegate {
   /**
    * This syntax method allows for a custom interpretation of the contents of
    * mustaches (`{{` ... `}}`).
    *
    * When a template is inserting an instance, it will invoke this method for
    * each mustache which is encountered. The function is invoked with four
    * arguments:
    *
    * - [model]: The data context for which this instance is being created.
    * - [path]: The text contents (trimmed of outer whitespace) of the mustache.
@@ skipping 28 matching lines @@
    *   instance.
    * - [model]: The data context for which this instance is being created.
    *
    * The template element will always use the return value of `getInstanceModel`
    * as the model for the new instance. If the syntax does not wish to override
    * the value, it should simply return the `model` value it was passed.
    */
   getInstanceModel(Element template, model) => model;
 }
 
-
 @Experimental()
 @DomName('HTMLTemplateElement')
 @SupportedBrowser(SupportedBrowser.CHROME)
 @Experimental()
 // https://dvcs.w3.org/hg/webcomponents/raw-file/tip/spec/templates/index.html#template-element
 class TemplateElement extends _HTMLElement native "HTMLTemplateElement" {
   // To suppress missing implicit constructor warnings.
   factory TemplateElement._() { throw new UnsupportedError("Not supported"); }
 
   @DomName('HTMLTemplateElement.HTMLTemplateElement')
@@ skipping 199 matching lines @@
 tr[template],
 td[template],
 caption[template],
 colgroup[template],
 col[template],
 option[template] {
   display: none;
 }''';
     document.head.append(style);
   }
-
-  /**
-   * A mapping of names to Custom Syntax objects. See [CustomBindingSyntax] for
-   * more information.
-   */
-  @Experimental()
-  static Map<String, CustomBindingSyntax> syntax = {};
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // WARNING: Do not edit - generated code.
 
 
 @DomName('Text')
 class Text extends CharacterData native "Text" {
@@ skipping 7750 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }