docs: protected void insertRelaxDefaultsComponent() {
      if (fRelaxDefaults == null) {
        fRelaxDefaults = new RelaxNGDefaultsComponent(resolver);
        addCommonComponent(fRelaxDefaults);
        fRelaxDefaults.reset(this);
      }
      XMLDocumentSource prev = fLastComponent;
      fLastComponent = fRelaxDefaults;
        
      XMLDocumentHandler next = prev.getDocumentHandler();
      prev.setDocumentHandler(fRelaxDefaults);
      fRelaxDefaults.setDocumentSource(prev);
      if (next != null) {
          fRelaxDefaults.setDocumentHandler(next);
          next.setDocumentSource(fRelaxDefaults);
      }
    }