Why do you need this filter?
It`s Easy, If you are a webmaster of "twitter" niche sites and you want to find link partners from your niche with PR5+ , and make sure those traffic are in your "traffic" level, you can easily do this by selecting any google pr you wish, Alexa rank, and get a full list of potential link partners.
Rank filter
Alexa Rank:(Lower Limit)
-(Higher Limit)
Google PR:
Tags filter