If the label has been set so that it has an mnemonic key (using i.
e. set_markup_with_mnemonic, set_text_with_mnemonic, Label.with_mnemonic or the “use_underline” property) the label can be associated with a widget that is the target of the mnemonic. When the label is inside a widget (like a Button or a Notebook tab) it is automatically associated with the correct widget, but sometimes (i.e. when the target is a Entry next to the label) you need to set it explicitly using this function.
The target widget will be accelerated by emitting the GtkWidget:
GtkLabel:mnemonic-activate signal on it. The default handler for
this signal will activate the widget if there are no mnemonic collisions and toggle focus between the colliding widgets otherwise.
the target Widget, or null to unset