'Append a group to the XLS data
@param rows: the XLS rows array to append to
@param group: the group dict
@param level: the grouping level'

def xls_group_data(self, rows, group, level=0):

    subgroups = group.get('d')
    items = group.get('i')
    if (self.group_headers and (level > 0)):
        self.xls_group_header(rows, group, level=level)
    if subgroups:
        for subgroup in subgroups:
            self.xls_group_data(rows, subgroup, level=(level + 1))
    elif items:
        for item in items:
            self.xls_item_data(rows, item, level=level)
    if (level > 0):
        self.xls_group_footer(rows, group, level=level)
