 single argument,
the plot data. The return value must be a <code>data.frame</code>, and
will be used as the layer data. A <code>function</code> can be created
from a <code>formula</code> (e.g. <code>~ head(.x, 10)</code>).</p></td>
    </tr>
    <tr>
      <th>geom</th>
      <td><p>Used geom, default to 'ribbon'</p></td>
    </tr>
    <tr>
      <th>position</th>
      <td><p>Position adjustment, either as a string, or the result of
a call to a position adjustment function.</p></td>
    </tr>
    <tr>
   