code: function augmentEdgesPipes(srcPipePrototype) {
    /**
     * Returns vertices at the tail of an edge.
     *  E.g. `A --> B - returns A`
     */
    srcPipePrototype.outV = function (filter) {
      return this.pipe(new EdgesToVerticesPipe(this._graph, 'out', filter));
    };
  
    /**
     * Returns vertices at the head of an edge.
     *  E.g. `A --> B - returns B`
     */
    srcPipePrototype.inV = function (filter) {
      return this.pipe(new EdgesToVerticesPipe(this._graph, 'in', filter));
    };
  
    /**
     * Returns both from and to vertices of an edge
     *  E.g. `A --> B - returns A and B`
     */
    srcPipePrototype.bothV = function (filter) {
      return this.pipe(new EdgesToVerticesPipe(this._graph, 'both', filter));
    };
  }
docs: Pipes which take edges as input ----------------------------------