code: function DelegateField(type, options) {
    Field.call(this, type, options);
    this.options = options;
    this.requisition.onAssignmentChange.add(this.update, this);
  
    this.element = util.createElement(this.document, 'div');
    this.update();
  
    this.onFieldChange = util.createEvent('DelegateField.onFieldChange');
  }
docs: A field that works with delegate types by delaying resolution until that
  last possible time