     //  imageDisplay
     //----------------------------------
     
-    [SkinPart(required="false")]
-    
-    /**
-     *  A skin part that defines image content.
+    [SkinPart(required="true")]
+    
+    /**
+     *  A required skin part that defines image content.
      *  
      *  @langversion 3.0
      *  @playerversion Flash 10

            if (BitFlagUtil.isSet(imageDisplayProperties as uint, HORIZONTAL_ALIGN_PROPERTY_FLAG))
                newImageDisplayProperties.horizontalAlign = imageDisplay.horizontalAlign;
            
            imageDisplayProperties = newImageDisplayProperties;
        }
    }

        }
        else if (instance == progressIndicator)
        {
            if (_loading && progressIndicator && imageDisplay)
                progressIndicator.value = percentComplete(imageDisplay.bytesLoaded, imageDisplay.bytesTotal);
        }
    }
