data fields which should
be treated as categorical.</p>

<p><code>ft_numeric()</code> - identifies data fields which contain numeric values that
should be treated as continuous. Any values which contain non-numeric
characters (including grouping marks) will be classed as non-conformant</p>
<p><code>ft_datetime()</code> - identifies data fields which contain date
values that should be treated as continuous.</p>
<p><code>ft_freetext()</code> - identifies data fields which contain
free text values. Only presen