[YouTube-API] How to fetch a YouTube "topic" feed?

How do you retrieve a list of videos that belong to a youtube topic?

I've scoured the API docs v1 and v2, tried guessing the uri, and done a lot of google searches. 

Here is an example:

http://www.youtube.com/topic/IGr3XQoJofY#feed 

note that it is not a search query, it is not a playlist. It is a "topic". I'm trying to use the gdata youtube api.

Thanks in advance,

- Fin

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