docs: public FastReportBuilder addGroups(int numgroups) {
  		groupCount = numgroups;
  		for (int i = 0; i < groupCount; i++) {
  			GroupBuilder gb = new GroupBuilder();
  			PropertyColumn col = (PropertyColumn) report.getColumns().get(i);
  			gb.setCriteriaColumn(col);
  			report.getColumnsGroups().add(gb.build());
  		}
  		return this;
  	}