     }
     
     /**
-     *  If viewport is non null then ask it to compute the verical
-     *  scroll position delta for step up/down.  The delta is added
-     *  to this scrollbar's value.  
-     * 
-     *  @see viewport
-     *  @see #setValue
-     *  @see IViewport#verticalScrollPositionDelta
+     *  If <code>viewport</code> is not null, 
+     *  change the vertical scroll position for line up or line down by 
+     *  scrolling the viewport.
+     *  This method calculates the amount to scroll by calling the 
+     *  <code>IViewport.verticalScrollPositionDelta()</code> method 
+     *  with either <code>flash.ui.Keyboard.RIGHT</code> 
+     *  or <code>flash.ui.Keyboard.LEFT</code>.
+     *  It then calls the <code>setValue()</code> method to 
+     *  set the <code>IViewport.verticalScrollPosition</code> property 
+     *  to the appropriate value.
+     *
+     *  <p>If <code>viewport</code> is null, 
+     *  change the vertical scroll position for line up or line down by calling 
+     *  the <code>step()</code> method.</p>
+     *
+     *  @param increase Whether the line scoll is up (<code>true</code>) or
+     *  down (<code>false</code>). 
+     * 
+     *  @see mx.components.baseClasses.FxTrackBase#step()
+     *  @see mx.components.baseClasses.FxTrackBase#setValue()
+     *  @see mx.core.IViewport
+     *  @see mx.core.IViewport#verticalScrollPosition
+     *  @see mx.core.IViewport#verticalScrollPositionDelta()
      */
     override public function step(increase:Boolean = true):void
     {

    //--------------------------------------------------------------------------

    /**
     *  The size of the track on a VScrollBar equals the height of the track.
     */
    override protected function get trackSize():Number
    {

    }
    
    /**
     *  Returns the position of the thumb button on an FxVScrollBar control, 
     *  which is equal to the <code>localY</code> parameter.
     * 
     *  @param localX The X position relative to the scrollbar control.
     *
     *  @param localY The Y position relative to the scrollbar control.
     *
     *  @return The position of the thumb button.
     */
    override protected function pointToPosition(localX:Number, 
                                                localY:Number):Number
