code: function SchemaType (path, options, instance) {
    this.path = path;
    this.instance = instance;
    this.validators = [];
    this.setters = [];
    this.getters = [];
    this.options = options;
    this._index = null;
    this.selected;
  
    for (var i in options) if (this[i] && 'function' == typeof this[i]) {
      // { unique: true, index: true }
      if ('index' == i && this._index) continue;
  
      var opts = Array.isArray(options[i])
        ? options[i]
        : [options[i]];
  
      this[i].apply(this, opts);
    }
  }
docs: SchemaType constructor
  
  @param {String} path
  @param {Object} [options]
  @param {String} [instance]
  @api public