twSumArray( aArray, nStart, nEnd )
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     Sum an Array of numerics or strings. For numbers the arithmetic
     sum is returned. For strings, the total length of the strings is
     returned.

       Arguments:

     aArray - 'A' Array to be summed.

     nStart - 'N' Start element. Defaults  to the first element.

     nEnd   - 'N' End element. Defaults to the last element.

       Return:

     Numeric.

       Example:

     nArraySum := twSumArray( aNumbers )

     nTotalLength := twSumArray( aStrings )