code: public void append(byte[] utf8, int start, int len) {
          setCapacity(length + len, true);
          System.arraycopy(utf8, start, bytes, length, len);
          length += len;
      }
docs: Append a range of bytes to the end of the given text
  @param utf8 the data to copy from
  @param start the first position to append from utf8
  @param len the number of bytes to append