Changes from code review
diff --git a/src/ProtocolBuffers.Serialization/Http/MessageFormatOptions.cs b/src/ProtocolBuffers.Serialization/Http/MessageFormatOptions.cs
index 4ee1889..72d7371 100644
--- a/src/ProtocolBuffers.Serialization/Http/MessageFormatOptions.cs
+++ b/src/ProtocolBuffers.Serialization/Http/MessageFormatOptions.cs
@@ -8,7 +8,7 @@
     /// <summary>

     /// Defines control information for the various formatting used with HTTP services

     /// </summary>

-    public struct MessageFormatOptions

+    public class MessageFormatOptions

     {

         /// <summary>The mime type for xml content</summary>

         /// <remarks>Other valid xml mime types include: application/binary, application/x-protobuf</remarks>