ARG([position][,option])

This function deals with the argument(s) passed into a REXX program,
function or subroutine. With no parameters, the result is the number of
arguments given; that is, the position of the last explicitly specified
argument. If the parameter "position" is given, then the result is the
"position"th argument string, or an empty string if the argument was
not supplied. If the option is supplied, its first character must be
"E" or "O", standing for "Exists" or "Omitted" respectively. The result
of the function is then 0 or 1, depending on whether the "position"th
argument string exists or was omitted, with 1 meaning that "option" is
true.

  Example: if a rexx function was called by: 
         foo(5,,7)
  then   arg()      = 3
         arg(1)     = 5
         arg(2,'e') = 0