Save a screen region for later display
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 Syntax

       H_SAVRGN( <nTop>, <nLeft>, <nBottom>, <nRight> ) -> cScreen

 Arguments:

     <nTop>, <nLeft>, <nBottom>, and <nRight> define the portion of the
     screen to save.  Allowable values are 0 through 255.
     If not passed, defaults are 0 , 0 , MAXROW() , MAXCOL()

 Returns:

     H_SAVRGN() returns the saved screen region and its coordinates
     as a character string.

 Description:

     H_SAVRGN() is similar to Clipper's SAVESCREEN(), but it saves the
     screen coordinates as well as the display information.  The saved
     area can be restored by passing the returned string to H_RSTRGN().

     Note that the strings returned from H_SAVRGN() and Clipper's
     SAVESCREEN() are not interchangeable.  A screen region saved with
     with H_SAVRGN() must be restored using H_RSTRGN().

     H_SAVRGN() calls Clipper's SAVESCREEN().  Refer to the Clipper
     documentation for more information regarding this function.

 Examples:

     The following example uses H_SAVRGN() and H_RSTRGN() to save
     and restore a portion of the screen.

     @ 00, 00, 24, 79 BOX "111111111"       // fill the screen with 1's
     cScreen = H_SAVRGN(10, 10, 20, 30)    // save a region
     @ 00, 00, 24, 79 BOX "222222222"       // fill the screen with 2's
     H_RSTRGN(cScreen)                     // restore the 1's region

 Source: SCREGION.PRG

 Author:  David A. Richardson