docs: function wb_sheet_idx(wb, sh) {
  	if(typeof sh == "number") {
  		if(sh >= 0 && wb.SheetNames.length > sh) return sh;
  		throw new Error("Cannot find sheet # " + sh);
  	} else if(typeof sh == "string") {
  		var idx = wb.SheetNames.indexOf(sh);
  		if(idx > -1) return idx;
  		throw new Error("Cannot find sheet name |" + sh + "|");
  	} else throw new Error("Cannot find sheet |" + sh + "|");
  }