Unity 3.5: What is the definition of PLE algorithm?

Hi, [Unity Roadmap 2011][1] -> Next release: Unity 3.5 -> Pathfinding states:

Unity will automatically generate navigation meshes from your level geometry.

Beautiful, natural-looking crowd simulation using RVO and PLE algorithms wrapped in a simple API. Agents can find paths to target locations with built-in crowd simulation, or can be moved directly on the NavMesh in a similar way to the character controller. I was able to identify RVO as "Reciprocal Velocity Obstacles" but couldn't find any PLE algorithm. I would greatly appreciate an answer including a source. Thank you. [1]: http://blogs.unity3d.com/2011/06/16/unity-roadmap-2011/