nodes drawn with top z-index on hovering over edge - when an edge is moused over, its source and target node will have the   highest z-value to improve visibility
nodes drawn with top z-index on hovering over edge
- when an edge is moused over, its source and target node will have the
  highest z-value to improve visibility

PathwayCommons/pathways-search,PathwayCommons/pathways-search