If there is a validity mask associated with the input object, the mask is
transferred to the output object.  To decrease processing time, the 
operation will still be performed on those data that have corresponding mask 
values equal to zero.  If the data under the mask is genuinely \fInot\fP 
processable, such as NaN or infinity, the user can specify a that a value 
be substituted in place of the original value when it is accessed.  The masked 
data substitution attributes for a data object can be explicitly set and 
stored using the \fISet Attribute\fP operator, DATAMANIP::ksetdattr. 
