getLabel
Fetches the text from a label widget.
This is including any embedded underlines indicating mnemonics and Pango markup, as set by method@Gtk.Expander.set_label. If the label text has not been set the return value will be null. This will be the case if you create an empty button with gtk_button_new() to use as a container.
Return
The text of the label widget. This string is owned by the widget and must not be modified or freed.