[Standards] Presence Priority Implementation Guide

[JD Conley]

> Really interesting set of rules.  There's at least one more axis I'd
> like to add, though.  I always want to prefer my desktop to my phone,
> unless I'm away from my desk.  I think this just argues that some
> devices have a negative bias built in on top of these rules.

Yeah, negative bias could do it. There is also the case when you
actually want your mobile device to take priority, but I think that is
user selected (hit a button on your phone), rather than system
determined. So something like:

Mobile device software, unlike desktop software, should not base its
priority on the level of system input activity. Typically a mobile
device is stowed away in your pocket until you wish to use it. Thus, the
mobile device software should announce initial availability at either 0
or -1.

When it receives presence from any peer, the mobile software must take
further action based on the highest priority peer. If the highest
priority peer's show value is away or xa, the mobile device should
increase its priority to 127, regardless of the priority of the peer.
However, if the highest priority peer does not have a show value of away
or xa, the mobile software should adjust its priority to either 0 or -1.

In some cases the user of the mobile device may wish to specify that she
will receive all messages on the device. In this case, the mobile device
should set its priority to 127.

If presence is received from a peer with a priority of 127, the receiver
must adjust its own priority below 127, if it isn't there already. This
is to insure the most active application receives the highest priority.
An application should never set its priority to 127, unless it is
absolutely certain that the resource is in fact the highest priority.

-JD