Adds a custom widget to a generated menubar.
For this to work, the menu model of @bar must have an item with a custom attribute that matches @id.
the GtkWidget to add
the ID to insert @child at
%TRUE if @id was found and the widget added
See Implementation
Adds a custom widget to a generated menubar.
For this to work, the menu model of @bar must have an item with a custom attribute that matches @id.