data[0]是什么意思

 $("#txtSearch").autocomplete(arrUserName,{
                    minChars: 0, //双击空白文本框时显示全部提示数据
                    formatItem: function (data, i, total) {
                        return "<I>" + data[0] + "</I>"; //改变匹配数据显示的格式
                    },
                    formatMatch: function (data) {
                        return data[0];
                    },
                    formatResult: function (data,i,total) {
                        return data[0];
                    }
                }).result(SearchCallback);