How to load a widget in an iframe?

This should be straightforward. At minimum, you'd probably want the widget's main content to render the host <iframe> and then a separate attachment vm to render the content within the iframe. So, you'd probably want something like:

<iframe src="$core_v2_encoding.HtmlAttributeEncode($core_v2_widget.GetExecutedFileUrl('content.vm'))"></iframe>

And then in content.vm, treat it as a normal velocity script which is executed. If the goal is similar to generic content, it could basically output content defined by the widget's configuration.

The trick here is to use GetExecutedFileUrl instead of GetFileUrl. When that URL is requested, it returns the result of executing the script instead of the URL of the script, itself. As an aside, this is also the primary way in which to provide custom callbacks, as used in many widgets.

Awesome, you saved me a lot of work (again).

Hello Michael. Its works. But iframe dont show own content in Edit Mode. Maybe you know how should I work with this? Thanks!

This is by design. The page edit mode sanitizes certain HTML elements to protect the editing experience, including iframes. It's possible to detect if a widget is rendering in edit mode in order to provide an alternate preview output in that scenario using the flag:

$core_v2_widget.IsInWidgetPreviewMode