'Render the group header (=group label)
@param row: the XLS rows array to append to
@param group: the group dict
@param level: the grouping level'

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

    columns = self.data.get('c')
    value = group.get('v')
    if (not value):
        value = ''
    row = {'_group': {'label': s3_unicode(s3_strip_markup(value)), 'span': len(columns), 'totals': False}, '_style': 'subheader'}
    rows.append(row)
