the use
    of other features.
    If the context is itself optional,
    then the value of <b>Req</b> actually indicates whether the feature is required
    if the indicated context exists.
  </li>
  <li>
    The <b>Assertion</b> column specifies the constraint which must be met.
    Note that this text may contain errors as it is automatically drawn
    from the specification source before ReSpec processing, so automatic
    content provided by ReSpec such as section headings will be missing.
    If the a