If there is a validity mask associated with any of the input objects, the 
resulting output object will have a mask.  The output object mask is the 
logical AND of the input object masks.  If only one input object has a mask, 
then the other input object's mask is assumed to be "all valid" (mask 
value = 1).  If a mask is resized for the operation, the mask padding value 
will be 1.
.sp
To decrease processing time, the operation will still be performed on data 
that have corresponding mask values equal to zero (invalid data).  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. 
