function write_biff_rec(ba/*:BufArray*/, type/*:number*/, payload, length/*:?number*/)/*:void*/ {
	var t/*:number*/ = 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*/, payload, length/*:?number*/)/*:void*/ {
	var len = length || (payload||[]).length || 0;
	if(len <= 8224) return write_biff_rec(ba, type, payload, len);
	var t = 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);
	write_Bes(val, t || 'b', out);
	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_comments_biff2(ba/*:BufArray*/, comments/*:Array<[Comment[], number, number]>*/) {
	comments.forEach(function(data) {
		var text = data[0].map(function(cc) { return cc.t; }).join("");
		// TODO: should '\n' be translated to '\r' to correct for Excel 5.0 bug when exporting to BIFF2/3 ?
		if(text.length <= 2048) return write_biff_rec(ba, 0x001C, write_NOTE_BIFF2(text, data[1], data[2]));
		write_biff_rec(ba, 0x001C, write_NOTE_BIFF2(text.slice(0, 2048), data[1], data[2], text.length));
		for(var i = 2048; i < text.length; i += 2048)
			write_biff_rec(ba, 0x001C, write_NOTE_BIFF2(text.slice(i, Math.min(i+2048, text.length)), -1, -1, Math.min(2048, text.length - i)));
	});
}

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 if(isNaN(v))
				write_biff_rec(ba, 0x0005, write_BIFF2BERR(R, C, 0x24, "e")); // #NUM!
			else if(!isFinite(v))
				write_biff_rec(ba, 0x0005, write_BIFF2BERR(R, C, 0x07, "e")); // #DIV/0!
			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 == null ? "" : String(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 = ws["!data"] != null;
	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);
	}
	var row = [], comments = [];
	for(var C = range.s.c; C <= range.e.c; ++C) cols[C] = encode_col(C);
	for(var R = range.s.r; R <= range.e.r; ++R) {
		if(dense) row = ws["!data"][R] || [];
		rr = encode_row(R);
		for(C = range.s.c; C <= range.e.c; ++C) {
			var cell = dense ? row[C] : ws[cols[C] + rr];
			if(!cell) continue;
			/* write cell */
			write_ws_biff2_cell(ba, cell, R, C, opts);
			if(cell.c) comments.push([cell.c, R, C]);
		}
	}

	/* ... 0x12 0x19 0x13 (Password) */
	write_comments_biff2(ba, comments);
	/* 0x3d (Window1) ... */
}

/* Based on test files */
function write_biff2_buf(wb/*:Workbook*/, opts/*:WriteOpts*/) {
	var o = opts || {};
	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, (o.biff == 4 ? 0x0409 : (o.biff == 3 ? 0x0209 : 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();
}

var b8oid = 1, b8ocnts/*:Array<[number, number, number]>*/ = [];
function write_MsoDrawingGroup() {
	var buf = new_buf(82 + 8 * b8ocnts.length);
	/* [MS-ODRAW] 2.2.12 OfficeArtDggContainer */
	buf.write_shift(2, 0x0F);
	buf.write_shift(2, 0xF000);
	buf.write_shift(4, 74 + 8 * b8ocnts.length);
	/* 2.2.48 OfficeArtFDGGBlock */
	{
		buf.write_shift(2, 0);
		buf.write_shift(2, 0xF006);
		buf.write_shift(4, 16 + 8 * b8ocnts.length);
		/* 2.2.47 OfficeArtFDGG */
		{
			buf.write_shift(4, b8oid);
			buf.write_shift(4, b8ocnts.length+1);
			buf.write_shift(4, b8ocnts.reduce(function(acc,x) { return acc+x[1]; }, 0));
			buf.write_shift(4, b8ocnts.length);
		}
		/* 2.2.46 OfficeArtIDCL + */
		b8ocnts.forEach(function(b8) {
			buf.write_shift(4, b8[0]);
			buf.write_shift(4, b8[2]);
		});
	}
	/* 2.2.9 OfficeArtFOPT */
	{
		buf.write_shift(2, 0x33); // 0x03 | (3 << 4)
		buf.write_shift(2, 0xF00B);
		buf.write_shift(4, 0x12); // 3 * 6
		/* 2.3.21.15 Text Boolean Properties */
		buf.write_shift(2, 0xBF); buf.write_shift(4, 0x00080008);
		/* 2.3.7.2 fillColor */
		buf.write_shift(2, 0x0181); buf.write_shift(4, 0x08000041);
		/* 2.3.8.1 lineColor */
		buf.write_shift(2, 0x01C0); buf.write_shift(4, 0x08000040);
	}
	/* 2.2.45 OfficeArtSplitMenuColorContainer */
	{
		buf.write_shift(2, 0x40);
		buf.write_shift(2, 0xF11E);
		buf.write_shift(4, 16);
		buf.write_shift(4, 0x0800000D);
		buf.write_shift(4, 0x0800000C);
		buf.write_shift(4, 0x08000017);
		buf.write_shift(4, 0x100000F7);
	}
	return buf;
}
function write_comments_biff8(ba/*:BufArray*/, comments/*:Array<[Comment[], number, number]>*/) {
	var notes/*:Array<RawData>*/ = [], sz = 0, pl = buf_array(), baseid = b8oid;
	var _oasc;
	comments.forEach(function(c, ci) {
		var author = "";
		var text = c[0].map(function(t) { if(t.a && !author) author = t.a; return t.t }).join("");
		++b8oid;

		/* 2.2.14 OfficeArtSpContainer */
		{
			var oasc = new_buf(0x96);
			oasc.write_shift(2, 0x0F);
			oasc.write_shift(2, 0xF004);
			oasc.write_shift(4, 0x96);
			/* 2.2.40 OfficeArtFSP */
			{
				oasc.write_shift(2, 0xca2); // 0x02 | (0xca << 4)
				oasc.write_shift(2, 0xF00A);
				oasc.write_shift(4, 8);
				oasc.write_shift(4, b8oid);
				oasc.write_shift(4, 0xA00);
			}
			/* 2.2.9 OfficeArtFOPT */
			{
				oasc.write_shift(2, 0xE3); // 0x03 | (14 << 4)
				oasc.write_shift(2, 0xF00B);
				oasc.write_shift(4, 0x54); // 14 * 6
				/* 2.3.21.1 ITxid */
				oasc.write_shift(2, 0x80); oasc.write_shift(4, 0);
				/* 2.3.21.12 txdir */
				oasc.write_shift(2, 0x8B); oasc.write_shift(4, 0x02);
				/* 2.3.21.15 Text Boolean Properties */
				oasc.write_shift(2, 0xBF); oasc.write_shift(4, 0x00080008);
				/* 2.3.6.30 cxk */
				oasc.write_shift(2, 0x0158); oasc.l += 4;
				/* 2.3.7.2 fillColor */
				oasc.write_shift(2, 0x0181); oasc.write_shift(4, 0x08000050);
				/* 2.3.7.4 fillBackColor */
				oasc.write_shift(2, 0x0183); oasc.write_shift(4, 0x08000050);
				/* 2.3.7.6 fillCrMod */
				oasc.write_shift(2, 0x0185); oasc.write_shift(4, 0x100000F4);
				/* 2.3.7.43 Fill Style Boolean Properties */
				oasc.write_shift(2, 0x01BF); oasc.write_shift(4, 0x00100010);
				/* 2.3.8.1 lineColor */
				oasc.write_shift(2, 0x01C0); oasc.write_shift(4, 0x08000051);
				/* 2.3.8.4 lineCrMod */
				oasc.write_shift(2, 0x01C3); oasc.write_shift(4, 0x100000F4);
				/* 2.3.13.2 shadowColor */
				oasc.write_shift(2, 0x0201); oasc.write_shift(4, 0x08000051);
				/* 2.3.13.4 shadowCrMod */
				oasc.write_shift(2, 0x0203); oasc.write_shift(4, 0x100000F4);
				/* 2.3.13.23 Shadow Style Boolean Properties */
				oasc.write_shift(2, 0x023F); oasc.write_shift(4, 0x00030001);
				/* 2.3.4.44 Group Shape Boolean Properties */
				oasc.write_shift(2, 0x03BF); oasc.write_shift(4, 0x00020000 | (c[0].hidden ? 2 : 0));
			}
			/* [MS-XLS] 2.5.193 OfficeArtClientAnchorSheet */
			{
				oasc.l += 2;
				oasc.write_shift(2, 0xF010);
				oasc.write_shift(4, 0x12);
				oasc.write_shift(2, 0x3); // do not move or size with cells
				oasc.write_shift(2, c[2] + 2); oasc.l += 2;
				oasc.write_shift(2, c[1] + 1); oasc.l += 2;
				oasc.write_shift(2, c[2] + 4); oasc.l += 2;
				oasc.write_shift(2, c[1] + 5); oasc.l += 2;
			}
			/* [MS-XLS] 2.5.194 OfficeArtClientData */
			{
				oasc.l += 2;
				oasc.write_shift(2, 0xF011);
				oasc.l += 4;
			}
			oasc.l = 0x96;
			if(ci == 0) /* write_biff_rec(pl, 0x003C, oasc); */ _oasc = oasc;
			else write_biff_rec(pl, 0x00EC, oasc);
		}
		sz += 0x96;

		/* [MS-XLS] 2.4.181 Obj */
		{
			var obj = new_buf(52); // 22 + 26 + 4
			/* [MS-XLS] 2.5.143 FtCmo */
			obj.write_shift(2, 0x15);
			obj.write_shift(2, 0x12);
			obj.write_shift(2, 0x19);
			obj.write_shift(2, b8oid);
			obj.write_shift(2, 0);
			obj.l = 22;
			/* [MS-XLS] 2.5.149 FtNts */
			obj.write_shift(2, 0x0D);
			obj.write_shift(2, 0x16);
			obj.write_shift(4, 0x62726272);
			obj.write_shift(4, 0x95374305);
			obj.write_shift(4, 0x80301328);
			obj.write_shift(4, 0x69696904 + b8oid*256);
			obj.write_shift(2,0);
			obj.write_shift(4,0);
			// reserved
			obj.l += 4;
			write_biff_rec(pl, 0x005D, obj);
		}

		/* [MS-XLS] 2.5.195 OfficeArtClientTextbox */
		{
			var oact = new_buf(8);
			oact.l += 2;
			oact.write_shift(2, 0xF00D);
			oact.l += 4;
			write_biff_rec(pl, 0x00EC, oact);
		}
		sz += 8;

		/* [MS-XLS] 2.4.329 TxO */
		{
			var txo = new_buf(18);
			txo.write_shift(2, 0x12);
			txo.l += 8;
			txo.write_shift(2, text.length);
			txo.write_shift(2, 0x10);
			txo.l += 4;
			write_biff_rec(pl, 0x01b6, txo);
			/* text continue record TODO: switch to wide strings */
			{
				var cont = new_buf(1 + text.length);
				cont.write_shift(1, 0);
				cont.write_shift(text.length, text, "sbcs");
				write_biff_rec(pl, 0x003C, cont);
			}
			/* formatting continue records */
			{
				var conf = new_buf(0x10);
				conf.l += 8;
				conf.write_shift(2, text.length);
				conf.l += 6;
				write_biff_rec(pl, 0x003C, conf);
			}
		}

		/* 2.4.179 Note */
		{
			var notesh = new_buf(12 + author.length);
			notesh.write_shift(2, c[1]);
			notesh.write_shift(2, c[2]);
			notesh.write_shift(2, 0 | (c[0].hidden ? 0 : 2));
			notesh.write_shift(2, b8oid);
			notesh.write_shift(2, author.length);
			notesh.write_shift(1, 0);
			notesh.write_shift(author.length, author, "sbcs");
			notesh.l ++;
			notes.push(notesh);
		}
	});
	/* [MS-ODRAW] 2.2.13 OfficeArtDgContainer */
	{
		var hdr = new_buf(80);
		hdr.write_shift(2, 0x0F)
		hdr.write_shift(2, 0xF002);
		hdr.write_shift(4, sz + hdr.length - 8);
		/* [MS-ODRAW] 2.2.49 OfficeArtFDG */
		{
			hdr.write_shift(2, 0x10);
			hdr.write_shift(2, 0xF008);
			hdr.write_shift(4, 0x08);
			hdr.write_shift(4, comments.length + 1);
			hdr.write_shift(4, b8oid);
		}
		/* [MS-ODRAW] 2.2.16 OfficeArtSpgrContainer */
		{
			hdr.write_shift(2, 0x0f);
			hdr.write_shift(2, 0xF003);
			hdr.write_shift(4, sz + 0x30);
			/* [MS-ODRAW] 2.2.14 OfficeArtSpContainer */
			{
				hdr.write_shift(2, 0x0f);
				hdr.write_shift(2, 0xF004);
				hdr.write_shift(4, 0x28);
				/* [MS-ODRAW] 2.2.38 OfficeArtFSPGR */
				{
					hdr.write_shift(2, 0x01);
					hdr.write_shift(2, 0xF009);
					hdr.write_shift(4, 0x10);
					hdr.l += 16;
				}
				/* [MS-ODRAW] 2.2.40 OfficeArtFSP */
				{
					hdr.write_shift(2, 0x02);
					hdr.write_shift(2, 0xF00A);
					hdr.write_shift(4, 0x08);
					hdr.write_shift(4, baseid);
					hdr.write_shift(4, 0x05);
				}
			}
		}
		write_biff_rec(ba, 0x00EC, /* hdr */ bconcat([hdr, _oasc]));
	}
	ba.push(pl.end());
	notes.forEach(function(n) { write_biff_rec(ba, 0x001C, n); });
	b8ocnts.push([baseid, comments.length + 1, b8oid]);
	++b8oid;
}

function write_FONTS_biff8(ba, data, opts) {
	write_biff_rec(ba, 0x0031 /* 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, 0x041E /* 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, 0x0867 /* 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, 0x0868 /* Feat */, o);
}

function write_CELLXFS_biff8(ba, opts) {
	for(var i = 0; i < 16; ++i) write_biff_rec(ba, 0x00e0 /* XF */, write_XF({numFmtId:0, style:true}, 0, opts));
	opts.cellXfs.forEach(function(c) {
		write_biff_rec(ba, 0x00e0 /* 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, 0x01b8 /* HLink */, write_HLink(HL));
		if(HL[1].Tooltip) write_biff_rec(ba, 0x0800 /* HLinkTooltip */, write_HLinkTooltip(HL));
	}
	delete ws['!links'];
}

function write_ws_cols_biff8(ba, cols) {
	if(!cols) return;
	var cnt = 0;
	cols.forEach(function(col, idx) {
		if(++cnt <= 256 && col) {
			write_biff_rec(ba, 0x007d /* 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, 0x0201 /* Blank */, write_XLSCell(R, C, os));
		return;
	}
	if(cell.bf) write_biff_rec(ba, 0x0006 /* 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;
			if(isNaN(v)) write_biff_rec(ba, 0x0205 /* BoolErr */, write_BoolErr(R, C, 0x24, os, opts, "e")); // #NUM!
			else if(!isFinite(v)) write_biff_rec(ba, 0x0205 /* BoolErr */, write_BoolErr(R, C, 0x07, os, opts, "e")); // #DIV/0!
			/* TODO: emit RK as appropriate */
			else write_biff_rec(ba, 0x0203 /* Number */, write_Number(R, C, v, os, opts));
			break;
		case 'b': case 'e':
			write_biff_rec(ba, 0x0205 /* BoolErr */, 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 == null ? "" : String(cell.v), opts.revStrings);
				write_biff_rec(ba, 0x00fd /* LabelSst */, write_LabelSst(R, C, isst, os, opts));
			} else write_biff_rec(ba, 0x0204 /* Label */, write_Label(R, C, (cell.v == null ? "" : String(cell.v)).slice(0,255), os, opts));
			break;
		default:
			write_biff_rec(ba, 0x0201 /* 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 = ws["!data"] != null;
	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, 0x000d /* CalcMode */, writeuint16(1));
	write_biff_rec(ba, 0x000c /* CalcCount */, writeuint16(100));
	write_biff_rec(ba, 0x000f /* CalcRefMode */, writebool(true));
	write_biff_rec(ba, 0x0011 /* CalcIter */, writebool(false));
	write_biff_rec(ba, 0x0010 /* CalcDelta */, write_Xnum(0.001));
	write_biff_rec(ba, 0x005f /* CalcSaveRecalc */, writebool(true));
	write_biff_rec(ba, 0x002a /* PrintRowCol */, writebool(false));
	write_biff_rec(ba, 0x002b /* PrintGrid */, writebool(false));
	write_biff_rec(ba, 0x0082 /* GridSet */, writeuint16(1));
	write_biff_rec(ba, 0x0080 /* Guts */, write_Guts([0,0]));
	/* DefaultRowHeight WsBool [Sync] [LPr] [HorizontalPageBreaks] [VerticalPageBreaks] */
	/* Header (string) */
	/* Footer (string) */
	write_biff_rec(ba, 0x0083 /* HCenter */, writebool(false));
	write_biff_rec(ba, 0x0084 /* VCenter */, writebool(false));
	/* ... */
	if(b8) write_ws_cols_biff8(ba, ws["!cols"]);
	/* ... */
	write_biff_rec(ba, 0x0200 /* Dimensions */, write_Dimensions(range, opts));
	/* ... */

	if(b8) ws['!links'] = [];
	var comments = [];
	var row = [];
	for(var C = range.s.c; C <= range.e.c; ++C) cols[C] = encode_col(C);
	for(var R = range.s.r; R <= range.e.r; ++R) {
		if(dense) row = ws["!data"][R] || [];
		rr = encode_row(R);
		for(C = range.s.c; C <= range.e.c; ++C) {
			ref = cols[C] + rr;
			var cell = dense ? row[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]);
			if(cell.c) comments.push([cell.c, R, C]);
		}
	}
	var cname/*:string*/ = _sheet.CodeName || _sheet.name || s;
	/* ... */
	if(b8) write_comments_biff8(ba, comments); else write_comments_biff2(ba, comments);
	/* ... */
	if(b8) write_biff_rec(ba, 0x023e /* Window2 */, write_Window2((_WB.Views||[])[0]));
	/* ... */
	if(b8 && (ws['!merges']||[]).length) write_biff_rec(ba, 0x00e5 /* MergeCells */, write_MergeCells(ws['!merges']));
	/* [LRng] *QUERYTABLE [PHONETICINFO] CONDFMTS */
	if(b8) write_ws_biff8_hlinks(ba, ws);
	/* [DVAL] */
	write_biff_rec(ba, 0x01ba /* CodeName */, write_XLUnicodeString(cname, opts));
	/* *WebPub *CellWatch [SheetExt] */
	if(b8) write_FEAT(ba, ws);
	/* *FEAT11 *RECORD12 */
	write_biff_rec(ba, 0x000a /* 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, 0x0087 /* Addin */);
	write_biff_rec(A, 0x00e1 /* InterfaceHdr */, b8 ? writeuint16(0x04b0) : null);
	write_biff_rec(A, 0x00c1 /* Mms */, writezeroes(2));
	if(b5) write_biff_rec(A, 0x00bf /* ToolbarHdr */);
	if(b5) write_biff_rec(A, 0x00c0 /* ToolbarEnd */);
	write_biff_rec(A, 0x00e2 /* InterfaceEnd */);
	write_biff_rec(A, 0x005c /* WriteAccess */, write_WriteAccess("SheetJS", opts));
	/* [FileSharing] */
	write_biff_rec(A, 0x0042 /* CodePage */, writeuint16(b8 ? 0x04b0 : 0x04E4));
	/* *2047 Lel */
	if(b8) write_biff_rec(A, 0x0161 /* DSF */, writeuint16(0));
	if(b8) write_biff_rec(A, 0x01c0 /* Excel9File */);
	write_biff_rec(A, 0x013d /* RRTabId */, write_RRTabId(wb.SheetNames.length));
	if(b8 && wb.vbaraw) write_biff_rec(A, 0x00d3 /* ObProj */);
	/* [ObNoMacros] */
	if(b8 && wb.vbaraw) {
		var cname/*:string*/ = _wb.CodeName || "ThisWorkbook";
		write_biff_rec(A, 0x01ba /* CodeName */, write_XLUnicodeString(cname, opts));
	}
	write_biff_rec(A, 0x009c /* BuiltInFnGroupCount */, writeuint16(0x11));
	/* *FnGroupName *FnGrp12 */
	/* *Lbl */
	/* [OleObjectSize] */
	write_biff_rec(A, 0x0019 /* WinProtect */, writebool(false));
	write_biff_rec(A, 0x0012 /* Protect */, writebool(false));
	write_biff_rec(A, 0x0013 /* Password */, writeuint16(0));
	if(b8) write_biff_rec(A, 0x01af /* Prot4Rev */, writebool(false));
	if(b8) write_biff_rec(A, 0x01bc /* Prot4RevPass */, writeuint16(0));
	write_biff_rec(A, 0x003d /* Window1 */, write_Window1(opts));
	write_biff_rec(A, 0x0040 /* Backup */, writebool(false));
	write_biff_rec(A, 0x008d /* HideObj */, writeuint16(0));
	write_biff_rec(A, 0x0022 /* Date1904 */, writebool(safe1904(wb)=="true"));
	write_biff_rec(A, 0x000e /* CalcPrecision */, writebool(true));
	if(b8) write_biff_rec(A, 0x01b7 /* RefreshAll */, writebool(false));
	write_biff_rec(A, 0x00DA /* 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, 0x0160 /* UsesELFs */, writebool(false));
	var a = A.end();

	var C = buf_array();
	/* METADATA [MTRSettings] [ForceFullCalculation] */
	if(b8) write_biff_rec(C, 0x008C /* Country */, write_Country());
	/* *SUPBOOK *LBL *RTD [RecalcId] *HFPicture */

	/* BIFF8: MsoDrawingGroup [*Continue] */
	if(b8 && b8ocnts.length) write_biff_rec(C, 0x00EB /* MsoDrawingGroup */, write_MsoDrawingGroup());
	/* BIFF8: [SST *Continue] ExtSST */
	if(b8 && opts.Strings) write_biff_continue(C, 0x00FC /* SST */, write_SST(opts.Strings, opts));

	/* *WebPub [WOpt] [CrErr] [BookExt] *FeatHdr *DConn [THEME] [CompressPictures] [Compat12] [GUIDTypeLib] */
	write_biff_rec(C, 0x000A /* 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, 0x0085 /* 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 bconcat(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 = dup(table_fmt);
	}
	if(wb && wb.SSF) {
		make_ssf(); SSF_load_table(wb.SSF);
		// $FlowIgnore
		o.revssf = evert_num(wb.SSF); o.revssf[wb.SSF[65535]] = 0;
		o.ssf = wb.SSF;
	}

	b8oid = 1; b8ocnts = [];
	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 bconcat(bufs);
}

function write_biff_buf(wb/*:Workbook*/, opts/*:WriteOpts*/) {
	for(var i = 0; i <= wb.SheetNames.length; ++i) {
		var ws = wb.Sheets[wb.SheetNames[i]];
		if(!ws || !ws["!ref"]) continue;
		var range = decode_range(ws["!ref"]);
		if(range.e.c > 255) { // note: 255 is IV
			if(typeof console != "undefined" && console.error) console.error("Worksheet '" + wb.SheetNames[i] + "' extends beyond column IV (255).  Data may be lost.");
		}
	}

	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");
}