Call other file html with metro ui JS Dialog

Guys do you know how to call external file for insert to dialog with Metro ui framework. I have followed docs here: http://metroui.org.ua/dialog.html But its not showing how to call external file like .html or .php. Please can you help me advice or solution.thanks

You can make an ajax call and set the result as content for the dialog on onShow event. [source]

$("#createFlatWindow").on('click', function(){
    $.Dialog({
        overlay: true,
        shadow: true,
        flat: true,
        icon: '<img src="images/excel2013icon.png">',
        title: 'Flat window',
        content: '',
        onShow: function(_dialog){
             $.ajax({
               url: "test.php", 
               dataType: "html",
               success: function(result){
                 var html = result;
                 $.Dialog.content(html);
               }
             });            
        }
    });
});