             maximum = viewport.contentHeight - viewport.height;
         }
     }
-    
+
     /**
      *  @private
      *  Scroll vertically by event.delta "steps".  This listener is added to both the scrollbar 

        if (event.isDefaultPrevented() || !vp || !vp.visible || !visible)
            return;
        
        var nSteps:uint = Math.abs(event.delta);
        var navigationUnit:uint;
        
        // Scroll event.delta "steps".  
        
        navigationUnit = (event.delta < 0) ? NavigationUnit.DOWN : NavigationUnit.UP;
        for (var vStep:int = 0; vStep < nSteps; vStep++)
        {
            var vspDelta:Number = vp.getVerticalScrollPositionDelta(navigationUnit);


import mx.core.IInvalidating;
import mx.core.mx_internal;
import mx.events.FlexMouseEvent;
import mx.events.PropertyChangeEvent;
import mx.events.ResizeEvent;

import spark.components.supportClasses.ScrollBarBase;
import spark.core.IViewport;
import spark.core.NavigationUnit;
import spark.utils.MouseEventUtil;

use namespace mx_internal;

//--------------------------------------
//  Events
//--------------------------------------

/**
 *  Dispatched when the <code>verticalScrollPosition</code> is going
 *  to change due to a <code>mouseWheel</code> event.
 * 
 *  <p>The default behavior is to scroll vertically by the event 
 *  <code>delta</code> number of "steps".  
 *  The viewport's <code>getVerticalScrollPositionDelta</code> method using 
 *  either <code>UP</code> or <code>DOWN</code>, depending on the scroll 
 *  direction, determines the height of the step.</p>
 * 
 *  <p>Calling the <code>preventDefault()</code> method
 *  on the event prevents the vertical scroll position from changing.
 *  Otherwise if you modify the <code>delta</code> property of the event,
 *  that value will be used as the number of vertical "steps".</p>
 *
 *  @eventType mx.events.FlexMouseEvent.MOUSE_WHEEL_CHANGING
 *  
 *  @langversion 3.0
 *  @playerversion Flash 10
 *  @playerversion AIR 2.5
 *  @productversion Flex 4.5
 */
[Event(name="mouseWheelChanging", type="mx.events.FlexMouseEvent")]

//--------------------------------------
//  Other metadata
