          let glob_group = (file, groupID, span_ids) => {
                    while (true) {
                        let group = file.g[groupID];
                        group.s.forEach(span_id => span_ids.add(span_id));
                        if (!group.e) {
                            break;
                        }
                        groupID = group.e;
                    };
                };

                let coverage_spans = (file, data, span_ids) => {
                    if (data.g != undef