The Sun Token [sab] (Sun always above/below the horizon) is used to display some text or symbol, if the date of the token corresponds to a date when the Sun is always above the horizon (ie. does not set) or always below the horizon (ie. does not rise).
The text or symbols that are to be displayed, and when, are determined by the settings specified in the Daylight tab of the Moon and Sun Options scriptline property, as shown below.
The calculations that determine on which dates the Sun is always above or below are performed based on the geographical locations selected in the Sun Data ScriptLine property.