code: protected String deriveHtmlFilePath(String bodyFile) {
          final String dirBase = bodyFile.contains("/") ? Srl.substringLastFront(bodyFile, "/") + "/" : "";
          final String pureFileName = Srl.substringLastRear(bodyFile, "/"); // same if no delimiter
          final String front = Srl.substringFirstFront(pureFileName, "."); // e.g. member_registration
          final String rear = Srl.substringFirstRear(pureFileName, "."); // e.g. dfmail or ja.dfmail
          return dirBase + front + "_html." + rear; // e.g. member_registration_html.dfmail
      }
docs: =============