Fixed: [ Issue 81 ] Protobuf editor does not understand full grammar for "extensions" decl.
https://code.google.com/p/protobuf-dt/issues/detail?id=81

com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext

diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext
index 8e73f49..1f4073b 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext
@@ -48,7 +48,13 @@
   Extensions | Type | Field | ExtendMessage | Option;
 
 Extensions:
-  'extensions' extensionsFrom=INT 'to' (extensionsTo=INT | 'max') ';';
+  'extensions' ranges+=Range (',' ranges+=Range)* ';';
+
+Range:
+  from=INT ('to' to=RangeMax)?;
+
+RangeMax:
+  INT | 'max';
 
 Field:
   Property | Group;