toggle
The "toggle" signal is emitted when the toggle() is called within the program, or when the user presses the enter or spacebar key while the connected GtkItem has focus.
Beyond that, this signal also has no behaviour defined at base level. In GtkListItem and GtkTreeItem, the "toggle" signal switches states between GTK_STATE_SELECTED and GTK_STATE_NORMAL; these GtkStateType enumerations are by default colour-coded, providing visual cues for the end user as well as a value within the program.
GtkMenuItem inherits the "toggle" signal without adding to it, i.e. it is there in theory but has no functionality in practice.
It is worth noting that both GtkListItem and GtkTreeItem are deprecated in future versions of GTK+, so that it would seem reasonable to expect the "toggle" signal to disappear too over time.
Callback function
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