How to use the asynciterator.MultiTransformIterator function in asynciterator

/*! @license MIT ©2014-2016 Ruben Verborgh, Ghent University - imec */
/* A ReorderingGraphPatternIterator builds bindings by reading matches for a basic graph pattern. */

var AsyncIterator = require('asynciterator'),
    TransformIterator = AsyncIterator.TransformIterator,
    MultiTransformIterator = AsyncIterator.MultiTransformIterator,
    rdf = require('../util/RdfUtil'),
    _ = require('lodash'),
    Logger = require('../util/ExecutionLogger')('ReorderingGraphPatternIterator');

var TriplePatternIterator = require('./TriplePatternIterator');

// Creates a new ReorderingGraphPatternIterator
function ReorderingGraphPatternIterator(parent, pattern, options) {
  // Empty patterns have no effect
  if (!pattern || !pattern.length)
    return new TransformIterator(parent, options);
  // A one-element pattern can be solved by a triple pattern iterator
  if (pattern.length === 1)
    return new TriplePatternIterator(parent, pattern[0], options);
  // For length two or more, construct a ReorderingGraphPatternIterator
  if (!(this instanceof ReorderingGraphPatternIterator))

/*! @license MIT ©2014-2016 Ruben Verborgh, Ghent University - imec */
/* A TriplePatternIterator builds bindings by reading matches for a triple pattern. */

var AsyncIterator = require('asynciterator'),
    MultiTransformIterator = AsyncIterator.MultiTransformIterator,
    rdf = require('../util/RdfUtil'),
    Logger = require('../util/ExecutionLogger')('TriplePatternIterator');

// Creates a new TriplePatternIterator
function TriplePatternIterator(parent, pattern, options) {
  if (!(this instanceof TriplePatternIterator))
    return new TriplePatternIterator(parent, pattern, options);
  MultiTransformIterator.call(this, parent, options);

  this._pattern = pattern;
  this._client = options && options.fragmentsClient;
}
MultiTransformIterator.subclass(TriplePatternIterator);

// Creates a transformer that extends upstream bindings with matches for the triple pattern.
// For example, if the iterator's triple pattern is '?s rdf:type ?o',