instanceOf in renaissance

I'm learning Objective C and the GNUStep development environment. For my project I'm using the Renaissance library for my GUI. The app will allow adjustments to an image's brightness, white balance, hue, etc. Following is an image of the interface I'm using for making adjustments to these various attributes.

The stepper and slider controls do not have a direct tag representation in gsmarkup, but using the control tag with the instanceOf attribute, the Renaissance library will create these controls. As the saying goes, an example is worth a thousand man pages:

Adjustments.gsmarkup

<?xml version="1.0"?>
<!DOCTYPE gsmarkup>
<gsmarkup>

<objects>
<window title="Image Adjustments" id="WindowAdjustments"  delegate="#NSOwner">
 <vbox>
  <box title="Brightness"><hbox>
    <control instanceOf="NSSlider" id="SliderBrightness" action="setBrightnessViaSlider:" height="28" width="256" />
    <textField id="TextBrightness" action="setBrightnessViaText:">000</textField>
    <control instanceOf="NSStepper" id="StepperBrightness" action="setBrightnessViaStepper:" height="28" width="18" />
  </hbox></box>
 </vbox>
</window>
 </objects>
<connectors>
<outlet source="#NSOwner" target="#SliderBrightness" key="SliderBrightness" />
<outlet source="#NSOwner" target="#TextBrightness" key="TextBrightness" />
<outlet source="#NSOwner" target="#StepperBrightness" key="StepperBrightness" />
</connectors>
</gsmarkup>

Adjustments.h

#import <AppKit/AppKit.h>
#import <Renaissance/Renaissance.h>

@interface Adjustments : NSObject
{
IBOutlet NSSlider *SliderBrightness;
IBOutlet NSTextField *TextBrightness;
IBOutlet NSStepper *StepperBrightness;
}

- (id) init;
- (void) dealloc;

- (void) setAdjustmentsDefaults;

- (void) setBrightnessViaSlider: (id)sender;
- (void) setBrightnessViaText: (id)sender;
- (void) setBrightnessViaStepper: (id)sender;
@end

Adjustments.m

#import <Adjustments.h>

@implementation Adjustments

- (id)init
{
if ((self = [super init]))
 {
   [NSBundle loadGSMarkupNamed:@"Adjustments" owner:self];
   [self setAdjustmentsDefaults];
 }
return self;
}

- (void)dealloc
{
[super dealloc];
}

- (void) setAdjustmentsDefaults
{
[SliderBrightness setMaxValue: 255];
[SliderBrightness setMinValue: 0];
[SliderBrightness setIntValue: 227];
[TextBrightness setIntValue: [SliderBrightness intValue]];
[StepperBrightness setMaxValue: [SliderBrightness maxValue]];
[StepperBrightness setMinValue:[SliderBrightness minValue]];
[StepperBrightness setIncrement: 1];
[StepperBrightness setIntValue: [SliderBrightness intValue]];
}

- (void) setBrightnessViaSlider: (id)sender
{
[StepperBrightness setIntValue: [SliderBrightness intValue]];
[TextBrightness setIntValue: [SliderBrightness intValue]];
}

- (void) setBrightnessViaText: (id)sender
{
[StepperBrightness setIntValue: [TextBrightness intValue]];
[SliderBrightness setIntValue: [TextBrightness intValue]];
}

- (void) setBrightnessViaStepper: (id)sender
{
[SliderBrightness setIntValue: [StepperBrightness intValue]];
[TextBrightness setIntValue: [StepperBrightness intValue]];
}

@end