GtkLabel, containing the text in str.gtkLabelNewWithMnemonic(str = NULL, show = TRUE)strstr are preceded by an underscore, they are
underlined. If you need a literal underscore character in a label, use
'__' (two underscores). The first underlined character represents a
keyboard accelerator called a mnemonic. The mnemonic key can be used
to activate another widget, chosen automatically, or explicitly using
gtkLabelSetMnemonicWidget.
If gtkLabelSetMnemonicWidget is not called, then the first
activatable ancestor of the GtkLabel will be chosen as the mnemonic
widget. For instance, if the label is inside a button or menu item,
the button or menu item will automatically become the mnemonic widget
and be activated by the mnemonic.