Fixes #347.

src/declaration/polymer-element.js

@@ -27,6 +27,8 @@
     createdCallback: function() {
       // fetch the element name
       this.name = this.getAttribute('name');
+      // fetch our extendee name
+      this.extends = this.getAttribute('extends');
       // install element definition, if ready
       this.registerWhenReady();
     },
@@ -35,8 +37,7 @@
       if (this.waitingForPrototype(this.name)) {
         return;
       }
-      // fetch our extendee name
-      var extendee = this.getAttribute('extends');
+      var extendee = this.extends;
       if (this.waitingForExtendee(extendee)) {
         //console.warn(this.name + ': waitingForExtendee:' + extendee);
         return;

src/declaration/prototype.js

@@ -114,7 +114,7 @@
     },
     // build prototype combining extendee, Polymer base, and named api
     generateBasePrototype: function(extnds) {
-      var prototype = memoizedBases[extnds];
+      var prototype = this.findBasePrototype(extnds);
       if (!prototype) {
         // create a prototype based on tag-name extension
         var prototype = HTMLElement.getPrototypeForTag(extnds);
@@ -125,6 +125,9 @@
       }
       return prototype;
     },
+    findBasePrototype: function(name) {
+      return memoizedBases[name];
+    },
     // install Polymer instance api into prototype chain, as needed 
     ensureBaseApi: function(prototype) {
       if (!prototype.PolymerBase) {
@@ -153,15 +156,26 @@
         prototype: this.prototype
       }
       // native element must be specified in extends
-      if (extendee && extendee.indexOf('-') < 0) {
-        info.extends = extendee;
+      var typeExtension = this.findTypeExtension(extendee);
+      if (typeExtension) {
+        info.extends = typeExtension;
       }
       // register the custom type
       this.ctor = document.register(name, info);
       // constructor shenanigans
       this.prototype.constructor = this.ctor;
       // register the prototype with HTMLElement for name lookup
       HTMLElement.register(name, this.prototype);
+    }, 
+    findTypeExtension: function(name) {
+      if (name && name.indexOf('-') < 0) {
+        return name;
+      } else {
+        var p = this.findBasePrototype(name);
+        if (p.element) {
+          return this.findTypeExtension(p.element.extends);
+        }
+      }
     }
   };
 

test/html/element-registration.html

@@ -31,6 +31,8 @@
   <x-blarg></x-blarg>
   <hr>
   <li is="my-li"></li>
+  <hr>
+  <li is="my-sub-li"></li>
 
   <!-- script follows declaration -->
   <polymer-element name="x-foo">
@@ -140,6 +142,12 @@
     </script>
   </polymer-element>
 
+  <polymer-element name="my-sub-li" extends="my-li" noscript>
+    <template>
+      Hello Sub World
+    </template>
+  </polymer-element>
+
   <script>
     var assert = chai.assert;
     function test() {
@@ -157,6 +165,8 @@
       assert.equal(zzif.squid, 'zink');
       var myLi = document.querySelector('[is=my-li]');
       assert.equal(myLi.custom, true);
+      var mySubLi = document.querySelector('[is=my-sub-li]');
+      assert.equal(mySubLi.custom, true);
       done();
     }
   </script>