@:build()

haxe
@:build(...)
class MyDialog extends Dialog { // thats it!
}

build=true

xml
<components>
    <class file="custom/custom1.xml" alias="CustomAlias" />
    <class folder="custom" />
</components>

// MyCustomDialog.xml
<dialog>
    <label id="bob" />
</dialog>

// module.xml
<components>
    <class file="MyCustomDialog.xml" />
</components>

// Main.hx
var d = new MyCustomDialog();
d.bob = "tim";
d.show();

<hbox width="100%" />

class MyComponent extends HBox {
    public function new() {
        percentWidth = 100;
    }
}

<vbox id="tim" />

class MyComponent extends VBox {
    public function new() {
        id = "tim;
    }
}

haxe
            main.findComponent("showDialog2", Button).onClick = function(e) {
                var dialog2 = new assets.custom.Test2();
                // wont work as the custom component isnt actually a dialog
                dialog2.show();
                
                // the actual dialog is a child now of the custom component from the xml file
                var actualDialog = dialog2.findComponent(Dialog);
                // also wont work as this isnt the custom component anymore, so build macro hasnt added fields
                //actualDialog.theValue.text = "The new value 2";
                actualDialog.show();
            }