gistfile1.m

@implentation UserForm
  - (SurveyTextField *)username
  {
    return SurveyDefineTextField(^(SurveyTextField  *field) {
      field.placeholder = @"username";
    });
  }
  
  
  // OR
  
  @dynamic username;
  
  - (void)setupFieldUsername:(SurveyTextField *field)
  {
    field.placeholder = @"username";
    field.onError = ^{
      field.backgroundColor = [UIColor redColor];
    };
  }
  
@end

// THIS
@dynamic username;

- (void)customizeFields
{
    self.username.placeholder = @"username";
    self.username.onError = ^{
        self.username.backgroundColor = [UIColor redColor];
    };
}