code: static int append(char[] src, char[] out, int j) {
          System.arraycopy(src, 0, out, j, src.length);
          return j + src.length;
      }
docs: Appends a source array verbatim to the output array. Caller must insure
  there is enough space in the array for the output.
  
  @param src the characters to copy
  @param out the output buffer
  @param j the offset where to write in the output buffer
  @return {@code j + src.length}