Bidding logic v3 return values

[typerat]

The generateBid function returns both an ad and a render URI in v3. What's the purpose of providing the URI separately, when it is already contained in the ad?
Is it possible/allowed to override the ad's URI in this way?

[cshmerling]

At the very least, the purpose of updating the return type for the bidding logic was to make it consistent with the requirements for generateBid in B&A. It would not be possible to modify the ad's URI at this point as the system will validate the render URL being present in the custom audience.

As for the design choice as to why they are returned this way, I'll have to dig up the reasoning.