or (const span of all_spans) {
                            let overlap = undefined;
                            for (const [_, child] of node.children) {
                                let child_overlap = child.overlaps.get(span);
                                child_overlap = (child_overlap == undefined) ? NONE_OVERLAP : child_overlap;
                                if (overlap == undefined) {
                                    overlap = child_overlap;
                                } else {
         