code: public function getContentTypeOptions()
      {
          $contentTypes = [
              self::CONTENT_TYPE_HTML  => __('HTML'),
              self::CONTENT_TYPE_CSS   => __('CSS'),
              self::CONTENT_TYPE_JS    => __('JavaScript'),
              self::CONTENT_TYPE_IMAGE => __('Images')
          ];
          return $contentTypes;
      }
docs: Get content types as option array
  
  @return array