docs: protected String expandToEquivalentUpcA(String content, boolean validate) {
  
          char[] upce = content.toCharArray();
          char[] upca = new char[11];
          Arrays.fill(upca, '0');
          upca[0] = upce[0];
          upca[1] = upce[1];
          upca[2] = upce[2];
  
          char emode = upce[6];
  
          switch (emode) {
              case '0':
              case '1':
              case '2':
                  upca[3] = emode;
                  upca[8] = upce[3];
                  upca[9] = upce[4];
                  upca[10] = upce[5];
                  break;
              case '3':
                  upca[3] = upce[3];
                  upca[9] = upce[4];
                  upca[10] = upce[5];
                  if (validate && (upce[3] == '0' || upce[3] == '1' || upce[3] == '2')) {
                      /* Note 1 - "X3 shall not be equal to 0, 1 or 2" */
                      throw new OkapiException("Invalid UPC-E data");
                  }
                  break;
              case '4':
                  upca[3] = upce[3];
                  upca[4] = upce[4];
                  upca[10] = upce[5];
                  if (validate && upce[4] == '0') {
                      /* Note 2 - "X4 shall not be equal to 0" */
                      throw new OkapiException("Invalid UPC-E data");
                  }
                  break;
              default:
                  upca[3] = upce[3];
                  upca[4] = upce[4];
                  upca[5] = upce[5];
                  upca[10] = emode;
                  if (validate && upce[5] == '0') {
                      /* Note 3 - "X5 shall not be equal to 0" */
                      throw new OkapiException("Invalid UPC-E data");
                  }
                  break;
          }
  
          return new String(upca);
      }