code: public void mergeFrom(Input input, final Object owner) throws IOException
      {
          final int first = input.readFieldNumber(this);
          if(first != ID_POJO)
              throw new ProtostuffException("order not preserved.");
          
          doMergeFrom(input, 
                  strategy.resolvePojoFrom(input, ID_POJO).getSchema(), 
                  owner);
      }
docs: Delegates to the schema derived from the input.
  The {@code owner} owns the message (polymorphic) that is tied to this schema.