Public Order Income Bonuses?

I've been seeing discussions online mentioning that, aside from the officially listed benefits high public order brings, i.e. growth, recruitment and building costs, the High Elves specifically also enjoy a certain income boost from a province if they manage to keep it at +100 public order. However, I cannot for the life of me find any official numbers or even a mention of this mechanic anywhere. Does anyone have the details, or perhaps an official source they can link me to? Thanks!