text: function write_biff_rec(ba/*:BufArray*/, type/*:number|string*/, payload, length/*:?number*/)/*:void*/ {
  	var t/*:number*/ = +type || +XLSRE[/*::String(*/type/*::)*/];
  	if(isNaN(t)) return;
  	var len = length || (payload||[]).length || 0;
  	var o = ba.next(4);
  	o.write_shift(2, t);
  	o.write_shift(2, len);
  	if(/*:: len != null &&*/len > 0 && is_buf(payload)) ba.push(payload);
  }
  
  function write_biff_continue(ba/*:BufArray*/, type/*:number|string*/, payload, length/*:?number*/)/*:void*/ {
  	var len = length || (payload||[]).length || 0;
  	if(len <= 8224) return write_biff_rec(ba, type, payload, len);
  	var t/*:number*/ = +type || +XLSRE[/*::String(*/type/*::)*/];
  	if(isNaN(t)) return;
  	var parts = payload.parts || [], sidx = 0;
  	var i = 0, w = 0;
  	while(w + (parts[sidx] || 8224) <= 8224) { w+= (parts[sidx] || 8224); sidx++; }
  	var o = ba.next(4);
  	o.write_shift(2, t);
  	o.write_shift(2, w);
  	ba.push(payload.slice(i, i + w));
  	i += w;
  	while(i < len) {
  		o = ba.next(4);
  		o.write_shift(2, 0x3c); // TODO: figure out correct continue type
  		w = 0;
  		while(w + (parts[sidx] || 8224) <= 8224) { w+= (parts[sidx] || 8224); sidx++; }
  		o.write_shift(2, w);
  		ba.push(payload.slice(i, i+w)); i+= w;
  	}
  }
  
  function write_BIFF2Cell(out, r/*:number*/, c/*:number*/) {
  	if(!out) out = new_buf(7);
  	out.write_shift(2, r);
  	out.write_shift(2, c);
  	out.write_shift(2, 0);
  	out.write_shift(1, 0);
  	return out;
  }
  
  function write_BIFF2BERR(r/*:number*/, c/*:number*/, val, t/*:?string*/) {
  	var out = new_buf(9);
  	write_BIFF2Cell(out, r, c);
  	if(t == 'e') { out.write_shift(1, val); out.write_shift(1, 1); }
  	else { out.write_shift(1, val?1:0); out.write_shift(1, 0); }
  	return out;
  }
  
  /* TODO: codepage, large strings */
  function write_BIFF2LABEL(r/*:number*/, c/*:number*/, val) {
  	var out = new_buf(8 + 2*val.length);
  	write_BIFF2Cell(out, r, c);
  	out.write_shift(1, val.length);
  	out.write_shift(val.length, val, 'sbcs');
  	return out.l < out.length ? out.slice(0, out.l) : out;
  }
  
  function write_ws_biff2_cell(ba/*:BufArray*/, cell/*:Cell*/, R/*:number*/, C/*:number*//*::, opts*/) {
  	if(cell.v != null) switch(cell.t) {
  		case 'd': case 'n':
  			var v = cell.t == 'd' ? datenum(parseDate(cell.v)) : cell.v;
  			if((v == (v|0)) && (v >= 0) && (v < 65536))
  				write_biff_rec(ba, 0x0002, write_BIFF2INT(R, C, v));
  			else
  				write_biff_rec(ba, 0x0003, write_BIFF2NUM(R,C, v));
  			return;
  		case 'b': case 'e': write_biff_rec(ba, 0x0005, write_BIFF2BERR(R, C, cell.v, cell.t)); return;
  		/* TODO: codepage, sst */
  		case 's': case 'str':
  			write_biff_rec(ba, 0x0004, write_BIFF2LABEL(R, C, (cell.v||"").slice(0,255)));
  			return;
  	}
  	write_biff_rec(ba, 0x0001, write_BIFF2Cell(null, R, C));
  }
  
  function write_ws_biff2(ba/*:BufArray*/, ws/*:Worksheet*/, idx/*:number*/, opts/*::, wb:Workbook*/) {
  	var dense = Array.isArray(ws);
  	var range = safe_decode_range(ws['!ref'] || "A1"), ref/*:string*/, rr = "", cols/*:Array<string>*/ = [];
  	if(range.e.c > 0xFF || range.e.r > 0x3FFF) {
  		if(opts.WTF) throw new Error("Range " + (ws['!ref'] || "A1") + " exceeds format limit A1:IV16384");
  		range.e.c = Math.min(range.e.c, 0xFF);
  		range.e.r = Math.min(range.e.c, 0x3FFF);
  		ref = encode_range(range);
  	}
  	for(var R = range.s.r; R <= range.e.r; ++R) {
  		rr = encode_row(R);
  		for(var C = range.s.c; C <= range.e.c; ++C) {
  			if(R === range.s.r) cols[C] = encode_col(C);
  			ref = cols[C] + rr;
  			var cell = dense ? (ws[R]||[])[C] : ws[ref];
  			if(!cell) continue;
  			/* write cell */
  			write_ws_biff2_cell(ba, cell, R, C, opts);
  		}
  	}
  }
  
  /* Based on test files */
  function write_biff2_buf(wb/*:Workbook*/, opts/*:WriteOpts*/) {
  	var o = opts || {};
  	if(DENSE != null && o.dense == null) o.dense = DENSE;
  	var ba = buf_array();
  	var idx = 0;
  	for(var i=0;i<wb.SheetNames.length;++i) if(wb.SheetNames[i] == o.sheet) idx=i;
  	if(idx == 0 && !!o.sheet && wb.SheetNames[0] != o.sheet) throw new Error("Sheet not found: " + o.sheet);
  	write_biff_rec(ba, 0x0009, write_BOF(wb, 0x10, o));
  	/* ... */
  	write_ws_biff2(ba, wb.Sheets[wb.SheetNames[idx]], idx, o, wb);
  	/* ... */
  	write_biff_rec(ba, 0x000A);
  	return ba.end();
  }
  
  function write_FONTS_biff8(ba, data, opts) {
  	write_biff_rec(ba, "Font", write_Font({
  		sz:12,
  		color: {theme:1},
  		name: "Arial",
  		family: 2,
  		scheme: "minor"
  	}, opts));
  }
  
  
  function write_FMTS_biff8(ba, NF/*:?SSFTable*/, opts) {
  	if(!NF) return;
  	[[5,8],[23,26],[41,44],[/*63*/50,/*66],[164,*/392]].forEach(function(r) {
  		/*:: if(!NF) return; */
  		for(var i = r[0]; i <= r[1]; ++i) if(NF[i] != null) write_biff_rec(ba, "Format", write_Format(i, NF[i], opts));
  	});
  }
  
  function write_FEAT(ba, ws) {
  	/* [MS-XLS] 2.4.112 */
  	var o = new_buf(19);
  	o.write_shift(4, 0x867); o.write_shift(4, 0); o.write_shift(4, 0);
  	o.write_shift(2, 3); o.write_shift(1, 1); o.write_shift(4, 0);
  	write_biff_rec(ba, "FeatHdr", o);
  	/* [MS-XLS] 2.4.111 */
  	o = new_buf(39);
  	o.write_shift(4, 0x868); o.write_shift(4, 0); o.write_shift(4, 0);
  	o.write_shift(2, 3); o.write_shift(1, 0); o.write_shift(4, 0);
  	o.write_shift(2, 1); o.write_shift(4, 4); o.write_shift(2, 0);
  	write_Ref8U(safe_decode_range(ws['!ref']||"A1"), o);
  	o.write_shift(4, 4);
  	write_biff_rec(ba, "Feat", o);
  }
  
  function write_CELLXFS_biff8(ba, opts) {
  	for(var i = 0; i < 16; ++i) write_biff_rec(ba, "XF", write_XF({numFmtId:0, style:true}, 0, opts));
  	opts.cellXfs.forEach(function(c) {
  		write_biff_rec(ba, "XF", write_XF(c, 0, opts));
  	});
  }
  
  function write_ws_biff8_hlinks(ba/*:BufArray*/, ws) {
  	for(var R=0; R<ws['!links'].length; ++R) {
  		var HL = ws['!links'][R];
  		write_biff_rec(ba, "HLink", write_HLink(HL));
  		if(HL[1].Tooltip) write_biff_rec(ba, "HLinkTooltip", write_HLinkTooltip(HL));
  	}
  	delete ws['!links'];
  }
  
  function write_ws_cols_biff8(ba, cols, ws) {
  	if(!cols) return;
  	var cnt = 0;
  	cols.forEach(function(col, idx) {
  		if(++cnt <= 256 && col) {
  			write_biff_rec(ba, "ColInfo", write_ColInfo(col_obj_w(idx, col), idx));
  		}
  	});
  }
  
  function write_ws_biff8_cell(ba/*:BufArray*/, cell/*:Cell*/, R/*:number*/, C/*:number*/, opts) {
  	var os = 16 + get_cell_style(opts.cellXfs, cell, opts);
  	if(cell.v == null && !cell.bf) {
  		write_biff_rec(ba, "Blank", write_XLSCell(R, C, os));
  		return;
  	}
  	if(cell.bf) write_biff_rec(ba, "Formula", write_Formula(cell, R, C, opts, os));
  	else switch(cell.t) {
  		case 'd': case 'n':
  			var v = cell.t == 'd' ? datenum(parseDate(cell.v)) : cell.v;
  			/* TODO: emit RK as appropriate */
  			write_biff_rec(ba, "Number", write_Number(R, C, v, os, opts));
  			break;
  		case 'b': case 'e':
  			write_biff_rec(ba, 0x0205, write_BoolErr(R, C, cell.v, os, opts, cell.t));
  			break;
  		/* TODO: codepage, sst */
  		case 's': case 'str':
  			if(opts.bookSST) {
  				var isst = get_sst_id(opts.Strings, cell.v, opts.revStrings);
  				write_biff_rec(ba, "LabelSst", write_LabelSst(R, C, isst, os, opts));
  			} else write_biff_rec(ba, "Label", write_Label(R, C, cell.v, os, opts));
  			break;
  		default:
  			write_biff_rec(ba, "Blank", write_XLSCell(R, C, os));
  	}
  }
  
  /* [MS-XLS] 2.1.7.20.5 */
  function write_ws_biff8(idx/*:number*/, opts, wb/*:Workbook*/) {
  	var ba = buf_array();
  	var s = wb.SheetNames[idx], ws = wb.Sheets[s] || {};
  	var _WB/*:WBWBProps*/ = ((wb||{}).Workbook||{}/*:any*/);
  	var _sheet/*:WBWSProp*/ = ((_WB.Sheets||[])[idx]||{}/*:any*/);
  	var dense = Array.isArray(ws);
  	var b8 = opts.biff == 8;
  	var ref/*:string*/, rr = "", cols/*:Array<string>*/ = [];
  	var range = safe_decode_range(ws['!ref'] || "A1");
  	var MAX_ROWS = b8 ? 65536 : 16384;
  	if(range.e.c > 0xFF || range.e.r >= MAX_ROWS) {
  		if(opts.WTF) throw new Error("Range " + (ws['!ref'] || "A1") + " exceeds format limit A1:IV16384");
  		range.e.c = Math.min(range.e.c, 0xFF);
  		range.e.r = Math.min(range.e.c, MAX_ROWS-1);
  	}
  
  	write_biff_rec(ba, 0x0809, write_BOF(wb, 0x10, opts));
  	/* [Uncalced] Index */
  	write_biff_rec(ba, "CalcMode", writeuint16(1));
  	write_biff_rec(ba, "CalcCount", writeuint16(100));
  	write_biff_rec(ba, "CalcRefMode", writebool(true));
  	write_biff_rec(ba, "CalcIter", writebool(false));
  	write_biff_rec(ba, "CalcDelta", write_Xnum(0.001));
  	write_biff_rec(ba, "CalcSaveRecalc", writebool(true));
  	write_biff_rec(ba, "PrintRowCol", writebool(false));
  	write_biff_rec(ba, "PrintGrid", writebool(false));
  	write_biff_rec(ba, "GridSet", writeuint16(1));
  	write_biff_rec(ba, "Guts", write_Guts([0,0]));
  	/* DefaultRowHeight WsBool [Sync] [LPr] [HorizontalPageBreaks] [VerticalPageBreaks] */
  	/* Header (string) */
  	/* Footer (string) */
  	write_biff_rec(ba, "HCenter", writebool(false));
  	write_biff_rec(ba, "VCenter", writebool(false));
  	/* ... */
  	if(b8) write_ws_cols_biff8(ba, ws["!cols"], ws);
  	/* ... */
  	write_biff_rec(ba, 0x200, write_Dimensions(range, opts));
  	/* ... */
  
  	if(b8) ws['!links'] = [];
  	for(var R = range.s.r; R <= range.e.r; ++R) {
  		rr = encode_row(R);
  		for(var C = range.s.c; C <= range.e.c; ++C) {
  			if(R === range.s.r) cols[C] = encode_col(C);
  			ref = cols[C] + rr;
  			var cell = dense ? (ws[R]||[])[C] : ws[ref];
  			if(!cell) continue;
  			/* write cell */
  			write_ws_biff8_cell(ba, cell, R, C, opts);
  			if(b8 && cell.l) ws['!links'].push([ref, cell.l]);
  		}
  	}
  	var cname/*:string*/ = _sheet.CodeName || _sheet.name || s;
  	/* ... */
  	if(b8) write_biff_rec(ba, "Window2", write_Window2((_WB.Views||[])[0]));
  	/* ... */
  	if(b8 && (ws['!merges']||[]).length) write_biff_rec(ba, "MergeCells", write_MergeCells(ws['!merges']));
  	/* [LRng] *QUERYTABLE [PHONETICINFO] CONDFMTS */
  	if(b8) write_ws_biff8_hlinks(ba, ws);
  	/* [DVAL] */
  	write_biff_rec(ba, "CodeName", write_XLUnicodeString(cname, opts));
  	/* *WebPub *CellWatch [SheetExt] */
  	if(b8) write_FEAT(ba, ws);
  	/* *FEAT11 *RECORD12 */
  	write_biff_rec(ba, "EOF");
  	return ba.end();
  }
  
  /* [MS-XLS] 2.1.7.20.3 */
  function write_biff8_global(wb/*:Workbook*/, bufs, opts/*:WriteOpts*/) {
  	var A = buf_array();
  	var _WB/*:WBWBProps*/ = ((wb||{}).Workbook||{}/*:any*/);
  	var _sheets/*:Array<WBWSProp>*/ = (_WB.Sheets||[]);
  	var _wb/*:WBProps*/ = /*::((*/_WB.WBProps||{/*::CodeName:"ThisWorkbook"*/}/*:: ):any)*/;
  	var b8 = opts.biff == 8, b5 = opts.biff == 5;
  	write_biff_rec(A, 0x0809, write_BOF(wb, 0x05, opts));
  	if(opts.bookType == "xla") write_biff_rec(A, "Addin");
  	write_biff_rec(A, "InterfaceHdr", b8 ? writeuint16(0x04b0) : null);
  	write_biff_rec(A, "Mms", writezeroes(2));
  	if(b5) write_biff_rec(A, "ToolbarHdr");
  	if(b5) write_biff_rec(A, "ToolbarEnd");
  	write_biff_rec(A, "InterfaceEnd");
  	write_biff_rec(A, "WriteAccess", write_WriteAccess("SheetJS", opts));
  	/* [FileSharing] */
  	write_biff_rec(A, "CodePage", writeuint16(b8 ? 0x04b0 : 0x04E4));
  	/* *2047 Lel */
  	if(b8) write_biff_rec(A, "DSF", writeuint16(0));
  	if(b8) write_biff_rec(A, "Excel9File");
  	write_biff_rec(A, "RRTabId", write_RRTabId(wb.SheetNames.length));
  	if(b8 && wb.vbaraw) write_biff_rec(A, "ObProj");
  	/* [ObNoMacros] */
  	if(b8 && wb.vbaraw) {
  		var cname/*:string*/ = _wb.CodeName || "ThisWorkbook";
  		write_biff_rec(A, "CodeName", write_XLUnicodeString(cname, opts));
  	}
  	write_biff_rec(A, "BuiltInFnGroupCount", writeuint16(0x11));
  	/* *FnGroupName *FnGrp12 */
  	/* *Lbl */
  	/* [OleObjectSize] */
  	write_biff_rec(A, "WinProtect", writebool(false));
  	write_biff_rec(A, "Protect", writebool(false));
  	write_biff_rec(A, "Password", writeuint16(0));
  	if(b8) write_biff_rec(A, "Prot4Rev", writebool(false));
  	if(b8) write_biff_rec(A, "Prot4RevPass", writeuint16(0));
  	write_biff_rec(A, "Window1", write_Window1(opts));
  	write_biff_rec(A, "Backup", writebool(false));
  	write_biff_rec(A, "HideObj", writeuint16(0));
  	write_biff_rec(A, "Date1904", writebool(safe1904(wb)=="true"));
  	write_biff_rec(A, "CalcPrecision", writebool(true));
  	if(b8) write_biff_rec(A, "RefreshAll", writebool(false));
  	write_biff_rec(A, "BookBool", writeuint16(0));
  	/* ... */
  	write_FONTS_biff8(A, wb, opts);
  	write_FMTS_biff8(A, wb.SSF, opts);
  	write_CELLXFS_biff8(A, opts);
  	/* ... */
  	if(b8) write_biff_rec(A, "UsesELFs", writebool(false));
  	var a = A.end();
  
  	var C = buf_array();
  	/* METADATA [MTRSettings] [ForceFullCalculation] */
  	if(b8) write_biff_rec(C, "Country", write_Country());
  	/* *SUPBOOK *LBL *RTD [RecalcId] *HFPicture *MSODRAWINGGROUP */
  
  	/* BIFF8: [SST *Continue] ExtSST */
  	if(b8 && opts.Strings) write_biff_continue(C, "SST", write_SST(opts.Strings, opts));
  
  	/* *WebPub [WOpt] [CrErr] [BookExt] *FeatHdr *DConn [THEME] [CompressPictures] [Compat12] [GUIDTypeLib] */
  	write_biff_rec(C, "EOF");
  	var c = C.end();
  
  	var B = buf_array();
  	var blen = 0, j = 0;
  	for(j = 0; j < wb.SheetNames.length; ++j) blen += (b8 ? 12 : 11) + (b8 ? 2 : 1) * wb.SheetNames[j].length;
  	var start = a.length + blen + c.length;
  	for(j = 0; j < wb.SheetNames.length; ++j) {
  		var _sheet/*:WBWSProp*/ = _sheets[j] || ({}/*:any*/);
  		write_biff_rec(B, "BoundSheet8", write_BoundSheet8({pos:start, hs:_sheet.Hidden||0, dt:0, name:wb.SheetNames[j]}, opts));
  		start += bufs[j].length;
  	}
  	/* 1*BoundSheet8 */
  	var b = B.end();
  	if(blen != b.length) throw new Error("BS8 " + blen + " != " + b.length);
  
  	var out = [];
  	if(a.length) out.push(a);
  	if(b.length) out.push(b);
  	if(c.length) out.push(c);
  	return __toBuffer([out]);
  }
  
  /* [MS-XLS] 2.1.7.20 Workbook Stream */
  function write_biff8_buf(wb/*:Workbook*/, opts/*:WriteOpts*/) {
  	var o = opts || {};
  	var bufs = [];
  
  	if(wb && !wb.SSF) {
  		wb.SSF = SSF.get_table();
  	}
  	if(wb && wb.SSF) {
  		make_ssf(SSF); SSF.load_table(wb.SSF);
  		// $FlowIgnore
  		o.revssf = evert_num(wb.SSF); o.revssf[wb.SSF[65535]] = 0;
  		o.ssf = wb.SSF;
  	}
  
  	o.Strings = /*::((*/[]/*:: :any):SST)*/; o.Strings.Count = 0; o.Strings.Unique = 0;
  	fix_write_opts(o);
  
  	o.cellXfs = [];
  	get_cell_style(o.cellXfs, {}, {revssf:{"General":0}});
  
  	if(!wb.Props) wb.Props = {};
  
  	for(var i = 0; i < wb.SheetNames.length; ++i) bufs[bufs.length] = write_ws_biff8(i, o, wb);
  	bufs.unshift(write_biff8_global(wb, bufs, o));
  	return __toBuffer([bufs]);
  }
  
  function write_biff_buf(wb/*:Workbook*/, opts/*:WriteOpts*/) {
  	var o = opts || {};
  	switch(o.biff || 2) {
  		case 8: case 5: return write_biff8_buf(wb, opts);
  		case 4: case 3: case 2: return write_biff2_buf(wb, opts);
  	}
  	throw new Error("invalid type " + o.bookType + " for BIFF");
  }
  