liarity stems from the retention of the &lt;exec&gt;
attributes for backwards compatibility.  Any file mapping is done
using a <CODE>null</CODE> sourcefile; therefore not all
<a href="../Types/mapper.html">Mapper</a> types will return
results.  When no results are returned, redirection specifications
will fall back to the task level attributes.  In practice this means that
defaults can be specified for input, output, and error output files.
</p>
<h3>Errors and return codes</h3>
By default the return code of