docs: function write_sty_xlml(wb, opts)/*:string*/ {
  	/* Styles */
  	var styles/*:Array<string>*/ = ['<Style ss:ID="Default" ss:Name="Normal"><NumberFormat/></Style>'];
  	opts.cellXfs.forEach(function(xf, id) {
  		var payload/*:Array<string>*/ = [];
  		payload.push(writextag('NumberFormat', null, {"ss:Format": escapexml(SSF._table[xf.numFmtId])}));
  		styles.push(writextag('Style', payload.join(""), {"ss:ID": "s" + (21+id)}));
  	});
  	return writextag("Styles", styles.join(""));
  }