Clarify how icecandidatepairnominate and selectCandidatePair are to be used

[jan-ivar]

I feel #174 merged without an explainer or example of its intended use, side-effects, or how to use it responsibly.

I've gotten some questions internally about when this API would be useful, and I couldn't immediately answer. The only situation they could think of was one where the service is operating on a particular network that it controls? Is that true? An explainer or intro or example to point at would be good.

A slide presented at TPAC says what the app can do:

Application can defer nomination of a candidate pair picked by the controlling ICE agent ...
Application can select any valid candidate pair to send data ...
Both controlling and controlled side can select a candidate pair to send data ...

But it doesn't say why or what problem is solved. The only use UDP port 3478 example given seems like it could be solved with {iceTransportPolicy: "relay"}, or by filtering icecandidate events, or am I missing something?

Application now has the responsibility & flexibility to synchronize send/receive ...

Can we lay out these responsibilities in an explainer with examples showing what's minimally needed to use the API correctly?