docs: function Brain(dataset) {
    // The root of the tree represents the start of the query.
    this.root = new Node(this)
  
    // List of token matchers: functions from tokens
    // (see src/tokenizers/tokenize.js)
    // to either nothing (if no match) or {tag, length, data}.
    this.tokenMatchers = tokenize.defaultTokenMatchers()
  
    // Number of examples per label.
    this.numExamples = new Map()
    // Are weights built?
    this.weightsNeedBuilding = true
    this.links = []
  
    this.learn = this.learn.bind(this)
    if (dataset != null) {
      dataset.forEach(this.learn)
    }
  }