Parses a string containing a UI definition, building only the requested objects and merges them with the current contents of this.
Upon errors false will be returned and throws will be assigned a `GError` from the gtk_builder_error or g_markup_error domain.
If you are adding an object that depends on an object that is not its child (for instance a `GtkTreeView` that depends on its `GtkTreeModel`),
you have to explicitly list all of them in
the string to parse
the length of
nul-terminated array of objects to build
true on success, false if an error occurred