graph.isNeighbor(elementA, elementB [, opt])

Return true if elementB is a neighbor of elementA. If opt.deep is set to true, take into account embedded elements.
If opt.outbound is set to true, return true only if elementB is a successing neighbor of elementA.
Similarly, if opt.inbound is set to true, return true only if elementB is a preceeding neighbor of elementA.