The “id” of the child defined in the template XML
Whether the child should be accessible as an “internal-child” when this class is used in GtkBuilder XML
The structure offset into the composite widget’s instance public or private structure where the automated child pointer should be set, or 0 to not assign the pointer.
3.10
Automatically assign an object declared in the class template XML to be set to a location on a freshly built instance’s private data, or alternatively accessible via gtk_widget_get_template_child().
The struct can point either into the public instance, then you should use G_STRUCT_OFFSET(WidgetType, member) for @struct_offset, or in the private struct, then you should use G_PRIVATE_OFFSET(WidgetType, member).
An explicit strong reference will be held automatically for the duration of your instance’s life cycle, it will be released automatically when #GObjectClass.dispose() runs on your instance and if a @struct_offset that is != 0 is specified, then the automatic location in your instance public or private data will be set to %NULL. You can however access an automated child pointer the first time your classes #GObjectClass.dispose() runs, or alternatively in #GtkWidgetClass.destroy().
If @internal_child is specified, #GtkBuildableIface.get_internal_child() will be automatically implemented by the #GtkWidget class so there is no need to implement it manually.
The wrapper macros gtk_widget_class_bind_template_child(), gtk_widget_class_bind_template_child_internal(), gtk_widget_class_bind_template_child_private() and gtk_widget_class_bind_template_child_internal_private() might be more convenient to use.
Note that this must be called from a composite widget classes class initializer after calling gtk_widget_class_set_template().