If the label has been set so that it has a mnemonic key (using i.e.
set_markup_with_mnemonic(), set_text_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
GTK2.Button or GTK2.Notebook tab) it is automatically associated with the
correct widget, but sometimes (i.e. when the target is a GTK2.Entry next
to the label) you need to set it explicitly using this function.
The target widget will be accelerated by emitting "mnemonic_activate" 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.
GTK2.Label()->set_max_width_chars()