code: function addCells (row, tidx, tend, textLines, change) {
  			if (tidx < tend) {
  				row.appendChild(telt("th", (tidx + 1).toString()));
  				row.appendChild(ctelt("td", change, textLines[tidx].replace(/\t/g, "\u00a0\u00a0\u00a0\u00a0")));
  				return tidx + 1;
  			} else {
  				row.appendChild(document.createElement("th"));
  				row.appendChild(celt("td", "empty"));
  				return tidx;
  			}
  		}
docs: Adds two cells to the given row; if the given row corresponds to a real
  line number (based on the line index tidx and the endpoint of the
  range in question tend), then the cells will contain the line number
  and the line of text from textLines at position tidx (with the class of
  the second cell set to the name of the change represented), and tidx + 1 will
  be returned.	 Otherwise, tidx is returned, and two empty cells are added
  to the given row.