11  Parameters
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     At the Clipper level, passing a parameter by reference means that
     Clipper will create a VREF (see above) and place it onto the Eval
     Stack before calling the function.  This allows the function
     (whether written in Clipper or C) to gain access to the variable.

     Passing by value, on the other hand, means that Clipper simply
     places a copy of the specified VALUE onto the Eval Stack.  Note, in
     particular, that passing a string by value does not mean that
     Clipper will make a duplicate copy of the string.  Only the VALUE
     (i.e., the OREF) is copied, not the string itself.