code: function(item, fieldName) {
  			if (fieldName === "FriendlyPath") { //$NON-NLS-0$
  				// Just update the "is valid" column
  				var rowNode = document.getElementById(this.myTree._treeModel.getId(item));
  				var oldCell = lib.$(".isValidCell", rowNode); //$NON-NLS-0$
  				var col_no = lib.$$array("td", rowNode).indexOf(oldCell); //$NON-NLS-0$
  				var cell = this.renderer.getIsValidCell(col_no, item, rowNode);
  				// replace oldCell with cell
  				oldCell.parentNode.replaceChild(cell, oldCell);
  			}
  		}
docs: Render the row of a single item, without rendering its siblings.