Want to know Navfn working in details!

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Hi, I want to change navfn package by modifying the plan method it uses.

Can you explain:

1. how calcNavFnDijkstra is utilized by makePlan()?
 2. how computePotential() helps to design the navigation function?
 3. how does default global planner wrapped around Dijkstra's algorithm?
 4. How does we actually get a global path? What parameters effects in making the global plan?
 5. In which situations  the plan generated by global planner can be bypassed by the TrajectoryPlannerROS ?

I am using ROS fuerte and Ubuntu 10.04

Thanks..