code: protected function getSchemaRequested()
      {
          $parts = $this->owner->getRequest()->getHeader(LeftAndMain::SCHEMA_HEADER);
          return !empty($parts);
      }
docs: Check if the current request has a X-Formschema-Request header set.
  Used by conditional logic that responds to validation results
  
  @todo Remove duplication. See https://github.com/silverstripe/silverstripe-admin/issues/240
  
  @return bool