Yii2, ExportMenu: How to format a date, that Excel recognise it automatically as date?
<p>I use in my grids the extension <a href="https://github.com/kartik-v/yii2-export" rel="nofollow">yii2-export</a> to export data to XLS and XLSX. Whatever I try, Excel does not automatically recognize the dates. I have tried e.g. the following columns formats:</p>

<pre><code>'mydate',  // yyyy-mm-dd
'mydate:date',   // dd.mm.yyyy
[
    'attribute' =&gt; 'mydate',
    'value' =&gt; function($model) {
        return date("m/d/Y",  strtotime($model-&gt;mydate));
    },
],   // mm/dd/yyyy
</code></pre>

<p>I suppose, I have to mark the dates as date. But how?</p>