understand the options of 'notify-send'

Question

I have gone through the man page for notify-send and I am not able to understand following two options

-u, --urgency=LEVEL Specifies the urgency level (low, normal, critical).
-h, --hint=TYPE:NAME:VALUE
          Specifies basic extra data to pass. Valid types are int, double, string and byte.

I believe the only use of urgency is to display a high urgency notification even if low urgency is in queue. But what are hints? I don't find any more info on it. Type I understand, but where will the NAME:VALUE be used?

Apart from above, the -t option says, "timeout in milliseconds", but I see notifications stay longer than given value. The given value is not even hounored. e.g I gave -t 400. The notification should be dismissed after 400 ms, but it goes after about 5 secs.

Any info on above posed questions?

Answer 1

This is half-way at best, but perhaps you find some help in it.

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There are two pieces to the puzzle notify-send and the notify-daemon or notification-server. Various implementations have various philosophies on what to include and how to use the different suggestions by the spec.

Implementations like NotifyOSD supply an option on the --expire-time with 0 or default -1. If value is 0 and alert box is used instead of notification, any other value is ignored – and server default used.

The --hint option can be used to send extra information on how to lay out custom alerts such as volume and brightness. For example:

notify-send "Vol" -i notification-audio-volume-medium -h int:value:55 -h string:x-canonical-private-synchronous:volume

show a volume notification with level set to 55.

As for the urgency level one thing, at least, is that it has an impact if other applications are running in full-screen mode. Games, video-player, (screen-saver?) etc. If Urgency level is low notifications are not displayed, if critical they are.