MSETBOUNDS()
 Set screen boundaries for the mouse cursor
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 Syntax

     MSETBOUNDS( [<nTop>], [<nLeft>], [<nBottom>],
        [<nRight>] ) --> NIL

 Arguments

     <nTop> defines the uppermost allowable screen row for the mouse
     cursor or 0 if omitted.  This value may range from 0 to the value of
     <nBottom>.

     <nLeft> defines the leftmost allowable screen column for the mouse
     or 0 if omitted.  This value may range from 0 to the value of <nRight>.

     <nBottom> defines the bottommost screen row for the mouse cursor or
     MaxRow() if omitted.  This value may range from the value of <nTop> to
     MaxRow().

     <nRight> defines the rightmost allowable screen column for the mouse
     or MaxCol() if omitted.  This value may range from the value of <nLeft>
     to MaxCol().

 Returns

     MSETBOUNDS() always returns NIL.

 Description

     MSETBOUNDS() is a function that is used for setting the region of the
     screen that the mouse cursor is restricted to.  The default at startup
     is the entire screen.  This setting is automatically maintained by the
     runtime's mouse subsystem when the screen mode is changed, for example,
     from the 50-line mode to the 25-line mode.