code: function() {
    if (! (this instanceof Chain)) {
      return new Chain();
    }
  
    this.validators = [];
    this.target = null;
    this.isOptional = false;
    this.isImmutable = false;
    this.isUpdateRequired = false;
    this._validatorCount = 0;
    this._numItemsValidator = null;
  }
docs: A validator chain object.  A new instance of this object must be placed at
  head of the list of validator functions for each key in a Valve schema.
  
  @constructor
  @return {Chain} A validator chain object.