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src/lib/style-transformer.html

@@ -252,6 +252,11 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
           } else {
             return hostScope + paren;    
           }
+        // if no paren, do a straight :host replacement.
+        // TODO(sorvell): this should not strictly be necessary but 
+        // it's needed to maintain support for `:host[foo]` type selectors
+        // which have been improperly used under Shady DOM. This should be
+        // deprecated.
         } else {
           return selector.replace(HOST, hostScope);
         }