Context of 'side', frac, in pgr_findClosestEdges

[nikmartin]

What is 'side' relative to in this function? In my scenario, if I click on the map and get a point, then pass that to pgr_findClosetEdges with no cap arg, I get an edge id, a side, and a frac. I think that frac is the % down the length edge that the point is closest to, relative to the lowest vertex? Is that correct? I'm making an assumption that frac is always from the vertex with the lowest value. Also, what is side useful for? 'l' and 'r' are relative to what? Is side relative to the orientation of the edge?