code: public void attachPlainText(String filenameOnHeader, InputStream resourceStream, String textEncoding) {
          assertArgumentNotEmpty("filenameOnHeader", filenameOnHeader);
          assertArgumentNotNull("resourceStream", resourceStream);
          assertArgumentNotEmpty("textEncoding", textEncoding);
          postcard.attachPlainText(filenameOnHeader, resourceStream, textEncoding);
      }
docs: ----------