Gtk composite template - Access to a ParentClass

I've tried to use composite templates in gtk, and as long as we don't need access to anything from outside of that template then it is fine. As soon as we try to have access to for example our parent widget, that is widget inside which is placed that composite class object, the problems begin.
Does anyone now how to access outside (parent) widget from composite class template?

For such specific questions, you are better off posting to the GNOME discourse, with Rust tag.

Thanks, will do that.