What do a notify-send notification category, hint and version parameters mean?

The notify-send command manual says Usage: notify-send [OPTION...] [BODY] - create a notification Help Options: -?, --help Show help options Application Options: -u, --urgency=LEVEL Specifies the urgency level (low, normal, critical). -t, --expire-time=TIME Specifies the timeout in milliseconds at which to expire the notification. -i, --icon=ICON[,ICON...] Specifies an icon filename or stock icon to display. -c, --category=TYPE[,TYPE...] Specifies the notification category. -h, --hint=TYPE:NAME:VALUE Specifies basic extra data to pass. Valid types are int, double, string and byte. -v, --version Version of the package. Meaning of the last 3 parameters: category, hint and version is unclear to me.