code: private int getLineBreakColumnIndex(int lineIndex) {
      int lineBreakIndex = lineBreakIndices.get(lineIndex);
      return (lineIndex == 0) ?
           lineBreakIndex : lineBreakIndex - lineBreakIndices.get(lineIndex - 1) - 1;
    }
docs: Gets the 0-based column number of the line break character for line identified by
  {@code lineIndex}.