anchor.diff:  
   header_syntax [Proto proto]
       :   SYNTAX ASSIGN STRING_LITERAL SEMICOLON! {
  -            if(! "proto2".equals(getStringFromStringLiteral($STRING_LITERAL.text)))
  -                throw new IllegalStateException("Syntax isn't proto2: '"+
  +            if(!"proto2".equals(getStringFromStringLiteral($STRING_LITERAL.text))) {
  +                throw new IllegalStateException("Syntax isn't proto2: '" +
                     getStringFromStringLiteral($STRING_LITERAL.text)+"'");
  +            }
                     
               if(!proto.annotations.isEmpty())
                   throw new IllegalStateException("Misplaced annotations: " + proto.annotations);
  
positive.code:                 proto.addExtension(extension);
              else
                  parent.addNestedExtension(extension);
          } (SEMICOLON?)!
      ;
      
  
negative.code:         (service_body[proto, service])+ RIGHTCURLY (SEMICOLON?)! {
              if(service.rpcMethods.isEmpty())
                  throw new IllegalStateException("Empty Service block: " + service.getName());
                  
              if(!proto.annotations.isEmpty())
                  throw new IllegalStateException("Misplaced annotations: " + proto.annotations);
          }
      ;
      
  