Parses a file containing a UI definition and merges it with the current contents of this.
This function is useful if you need to call [method@Gtk.Builder.set_current_object]) to add user data to callbacks before loading GtkBuilder UI. Otherwise, you probably want [ctor@Gtk.Builder.new_from_file] instead.
If an error occurs, 0 will be returned and throws will be assigned a `GError` from the `GTK_BUILDER_ERROR`, `G_MARKUP_ERROR` or `G_FILE_ERROR` domains.
It’s not really reasonable to attempt to handle failures of this call. You should not use this function with untrusted files (ie: files that are not part of your application). Broken `GtkBuilder` files can easily crash your program, and it’s possible that memory was leaked leading up to the reported failure. The only reasonable thing to do when an error is detected is to call `g_error()`.
the name of the file to parse
true on success, false if an error occurred