docs: public T headerFragment(Object model, Marshaller marshaller) {
          StringResult result = new StringResult();
  
          try {
              marshaller.marshal(model, result);
          } catch (XmlMappingException e) {
              throw new CitrusRuntimeException("Failed to marshal object graph for message header data", e);
          } catch (IOException e) {
              throw new CitrusRuntimeException("Failed to marshal object graph for message header data", e);
          }
  
          return header(result.toString());
      }