      th.setAttribute("colspan", cell.span)
                    let colId = cell.id
                    let col = df.cols[colId];
                    if (!cell.empty) {
                        if (col.children.length === 0) {
                            th.innerHTML = col.name
                        } else {
                            let link = document.createElement("a")
                            link.className = "expander"
                            let that = this
                            link.o