code: function (config) {
    var builder = new lunr.Builder
  
    builder.pipeline.add(
      lunr.trimmer,
      lunr.stopWordFilter,
      lunr.stemmer
    )
  
    builder.searchPipeline.add(
      lunr.stemmer
    )
  
    config.call(builder, builder)
    return builder.build()
  }
docs: A convenience function for configuring and constructing
  a new lunr Index.
  
  A lunr.Builder instance is created and the pipeline setup
  with a trimmer, stop word filter and stemmer.
  
  This builder object is yielded to the configuration function
  that is passed as a parameter, allowing the list of fields
  and other builder parameters to be customised.
  
  All documents _must_ be added within the passed config function.
  
  @example
  var idx = lunr(function () {
  this.field('title')
  this.field('body')
  this.ref('id')
  
  documents.forEach(function (doc) {
  this.add(doc)
  }, this)
  })
  
  @see {@link lunr.Builder}
  @see {@link lunr.Pipeline}
  @see {@link lunr.trimmer}
  @see {@link lunr.stopWordFilter}
  @see {@link lunr.stemmer}
  @namespace {function} lunr