    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`.