le and nested
      <code>&lt;arg&gt;</code> elements instead</b>.</td>
    <td align="center" rowspan="2">Exactly one of the two.</td>
  </tr>
  <tr>
    <td valign="top">executable</td>
    <td valign="top">the command to execute without any command line
      arguments.</td>
  </tr>
  <tr>
    <td valign="top">dir</td>
    <td valign="top">the directory in which the command should be executed.</td>
    <td align="center" valign="top">No</td>
  </tr>
  <tr>
    <td valign="top">os</td>
    <td valign="top