code: function setFlexible(b) {
    this.errorCallback = b ? onError.silent : onError.throw
    _.forEach(this.references, r => r.errorCallback = this.errorCallback)
    _.forEach(this.attributes, r => r.errorCallback = this.errorCallback)
  }
docs: Decide whether whether or not type will becheck for attributes and
  references of a whole class.
  @method
  @memberof Class~ClassInstance
  @param {boolean} b - If true, type is not checked on assignement,
  if false wrong assignement type riase an error.