GtkSpinButton::set_update_policy
There are only two possible settings for the spinbutton update policy.
Setting it as GTK_UPDATE_IF_VALID prevents the
current value from being changed where the newly entered value is
outside the range determined by the underlying
GtkAdjustment.
The default setting is GTK_UPDATE_ALWAYS, which
allows the update to continue by replacing an invalid value with
the value of the nearest range boundary.
Note that set_value() .
overrides the update policy setting.
