pacakge</td>
  </tr>
  <tr>
    <td>description</td>
    <td>required</td>
    <td>Each package SHALL have a human language description of the contents of the package</td>
  </tr>
  <tr>
    <td><b>canonical</b></td>
    <td>conditionally required</td>
    <td>The canonical URL for the Implementation guide represented by the package, if this package represents a single Implementation Guide. This SHALL be present if the package is for an Implementation Guide and is optional for other packages.</td>