code: public static boolean isBase64(final byte octet) {
          return octet == PAD_DEFAULT || (octet >= 0 && octet < DECODE_TABLE.length && DECODE_TABLE[octet] != -1);
      }
docs: Returns whether or not the <code>octet</code> is in the base 64 alphabet.
  
  @param octet
  The value to test
  @return {@code true} if the value is defined in the the base 64 alphabet, {@code false} otherwise.
  @since 1.4