docs: function getColumnAfter(lineIndex, columnIndex) {
      if (lineIndex in lines) {
        var line   = lines[lineIndex];
        var count  = 0;
        var offset = 0;
        for (var i = 0; i < line.length; i++) {
          var widthBefore = getBefore(line[i]).length;
          var widthAfter  = getAfter(line[i]).length;
          var nextCount   = count + widthBefore;
          if (nextCount > columnIndex) {
            break;
          } else {
            count   = nextCount;
            offset += widthAfter - widthBefore;
          }
        }
        return columnIndex + offset;
      } else {
        throw new Error('Line index is out of range');
      }
    }