OutcomePriorFeatureGenerator explanation?

[Jim foo.bar]

Hi guys,

I' can't figure out for the life of me what this feature-generator does! 
I originally thought it was generating features based on the outcome of 
a previous token but that is what PreviousMapFeatureGenerator does... 
The docs state:

"The definition feature maps the underlying distribution of outcomes."

What does that mean? This description is somewhat different from all the 
rest...

thanks in advance,

Jim