Scrollbar -- Overview
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 Class Function

 ScrollBar()     Create a new ScrollBar object
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 Exported Instance Variables

 barLength       Marks number of positions scroll bar client area occupies
 bitmaps         An array of bitmap files to be displayed
 cargo           User-definable variable
 colorSpec       Indicates the colors used by the ScrollBa:display() method
 current         Indicates number of current item the scroll bar refers to
 end             Indicates the screen position of the scroll bar's next arrow
 offset          Indicates column or row of vertical or horizontal scroll bar
 orient          Indicates if scroll bar is vertically/horizontally oriented
 sBlock          Code block evaluated at every state change
 start           Indicates the screen position of scroll bar's previous arrow
 style           Indicates characters used by the ScrollBar:display() method
 thumbPos        Indicates relative position of the thumb within scroll bar
 total           Indicates the total number of items the scroll bar refers to
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 Exported Methods

 display()       Shows a scroll bar, including its thumb, on the screen
 update()        Changes the thumb position on the screen
 hitTest()       Indicates position of mouse cursor relative to scroll bar